Picture of The ValveLiTzer: Low-voltage Tube Booster
Here's a little tube booster project for guitarists. It colors the sound with some tube distortion (although it's more an overdrive than a distortion pedal), a little compression, and it boosts the signal, too. It's a "dirty boost," with the flavor of tubes, and can really spice up an amp (and it does add punch.)

Now With More Gain!
Updated schematic added, see the last page...

Plus, it's low-voltage--no more than 13V, so it's perfectly safe for "tube neophytes" to build. No high-voltage dangers with this one. It can even be powered with a 9V battery (but read the step on "Powering Options.")

With only a few inexpensive parts and a simple circuit, this should be an easy first-time tube project!

I didn't use a video cam mic, so the "youtube" audio is halfway-decent quality. But the mp3 file (look below, beneath the pictures) is much better...it's same audio track.

Step 1: Background

Picture of Background
Vacuum tubes have an interesting characteristic called "starved cathode" operation, which results in a good deal of distortion when the tubes are run at very low voltages. Matsumin's Valve Caster tube booster was my introduction to low-voltage tube projects. These voltages, in fact, are so low that many old-skewl electronic techs would tell you that the tubes shouldn't even work... But they do (some do, anyway.) Ignoring the normal plate voltages, if run at 9V the filament voltages are so low that the heater filaments shouldn't even function (but they do.)

Matsumin's project uses 12AU7 tubes, and is a very worthy build. This build, the ValveLiTzer, uses a slightly more oddball tube: the 12FQ8. Why use a weird tube? Because I have about 25 of 'em, and no guitar amps or stompboxes use them. So why not build something?

But the 12FQ8 isn't a typical audio tube. It's a twin-triode, but with 4 plates, and a single shared cathode. Would it even work as an audio amplifier? Only one way to find out...

Why the name ValveLiTzer? These tubes came from the tone generator in a defunct WurliTzer organ.

There are a few web comments (re: are 12FQ8's appropriate for guitar amp use?) but no one to my knowledge actually has to date. Certainly more complex applications are possible.

See they next page for info on procuring the tube (unless you find an old WurliTzer...)
Nate Palsa3 months ago
Such a cool project! I've been looking for a small 12vdc unit to run in front of a class-D amp for a while and this one looks like it'll work wonderfully! I would probably opt for the low gain mod as I am just trying to add a little tube coloration to a small boombox. Therefore, opting out of the volume pot since the chip amp will handle that. The bias pot seems like a nice feature to retain however.

What would you recommend to use this with a stereo input signal? Is the 12FQ8 capable of that or do I need to use another tube?

gmoon (author)  Nate Palsa3 months ago

Thanks! I'd probably recommend you go ahead and have an adjustable gain and a volume control, but via trim pots that you can set internally and then leave as-is. Or set via fixed resistive dividers (breadboard it for the correct values). This approach will give you the best signal-to-noise.

To retain a stereo output, one of these tube preamps per channel (two separate preamps) will be needed.

If the Ible doesn't make it clear, definitely use a regulated supply... Good luck!

PaulK85 months ago

Sorry if this is a silly question, but would this pedal work well with my solid state amp? Or does it need to run through a tube amp, like a tube screamer?

gmoon (author)  PaulK85 months ago

YMMV. It will work with a solid state amp. As to whether you like how it sounds with a particular amp or not, that's subjective.

I'd guess that it wouldn't add much hair to the sound of SS amps. A little, maybe. A boost over unity, yes. Some tubeishness (whatever that is), yeah. But the Tube Screamer analogy is a good one, probably.

PaulK8 gmoon5 months ago

Ok, not what I thought you were gonna say hahaha, I thought you were gonna say that the pedal is meant for SS amps, to be like a tube amp emulator if you will.

If I were going to make one of these It would be for loads of fuzzy fuzz. Check out a band called Conan on youtube, that sort of super fuzz. I guess it would prob work for that more so than for the hard driven bluesy sort of sound.

gmoon (author)  PaulK85 months ago

This probably isn't the pedal for metal. I listened to Conan for a bit, and that's a more modern "scooped" metal sound, more common for post thrash and speed metal.

I'm not even sure what pedal would get that with a SS amp. You'll have to experiment. Distortion is a strange beast. Often times what sounds good at bedroom levels solo, sounds like crap at high volume with bass and drums.

My own taste in metal runs toward doom, and back to early Sabbath, etc., records...

On step 4, you refer to an SPDT switch as an "ON/ON SPST switch". By definition, that is not an SPST switch. I feel like that could trip up some less experienced makers.
gmoon (author)  chris.patrick.94617 months ago

That's probably correct, although SPDT doesn't describe the switch either, as there isn't a "dual" position for the actuator--it's a footswitch, and you can't know the current state of the switch visually.

Maybe "Latching double throw" would be best...

Why would those characteristics make it not count as a Single-Pole, Double-Throw switch? Great instructable btw; I'm building one now.
gmoon (author)  chris.patrick.94617 months ago

It does describe it electrically, but still doesn't adequately describe the switch used, 'cause it's latching, not double-throw.

Thanks! I think I need to revisit this one and play with the circuit a little for fun...

bmostert10 months ago
Hello! Just built the 0.4 version, this is my first stompbox project and it was a lot of fun! :) I got about half of it working, I need some help getting the rest of it to work as im really new to electronics. My switch is dead on the off position and on the on position (or maybe its the bipass?) Only the 500K audio pot works. Even when I touch the leads on the bias and gain pots I get nothing (no noise). Id really appreciate any help.
gmoon (author)  bmostert10 months ago

Hmmm. The gain pot shouldn't work in bypass mode at all, but if the signal is going through the tube (your tests suggest is isn't) something is wired wrong.

You worked off the wiring diagram? First off, does the filament glow? Check and recheck the wiring...

CarterBond1 year ago

I think I shall try this. I have Red and Orange metal project box, it should go nicely in it.

than891 year ago

Hey everyone, hope all is well!! Just built this bad boy (2pot version).. It seems to work fine, but the bias pot doesn't do anything but stopping the sound when i turn it all the way up (the valve looks brighter too). It also takes a few seconds for the sound to disappear, few seconds for it to appear again when I turn it back down... Any suggestions? I'm clueless.. Thanks a lot

gmoon (author)  than891 year ago

Not sure what's going on here...

The bias pot won't appear to do much if the gain is low--which you can of course hard-wire so it's low gain all the time. I'd suggest looking at the wiring of both pots to be sure it's correct.

robot7971 year ago
after lisening to this verry verry carfully
it sound like the base is a little bit to much distorted
it sounds nice
heck it even sounds like a old style amp
but a little distorted
cmpmuller1 year ago
Hi ! I've built this according to the V.04, and it works great..But :-) in a chain, I have a true bypass pedal after it, and unless it is on, or unless I have another buffered pedal after it in the chain, I lose a lot of clarity and output with the valvelitzer engaged. Do you know the input impedance ? (I saw that the output impedance is around 30-60K, any way to lower that? ) I am running a tillman preamp first in the chain, then 2 more true bypass pedals and a buffered one. Somehow the impedance chain seems to be messed up this way.
gmoon (author)  cmpmuller1 year ago
Hey, cmpmuller.

Yeah, I'd guess the output impedance is something like 60K, based on similar values for triode stages (even though this is an oddball tube). But a typical triode gain stage in a fender has something like 40K output impedance. So it's a tube thing--unless there's a cathode follower after the gain stage to drop the impedance, it's gonna need a high input impedance after to maintain the high end.

If you're OK with buffering, you could add an emitter follower (transistor) or an opamp after the tube to drop the output impedance.

Another thing to try would be a "brighness switch", which would add a small cap from C2 to the wiper of the volume pot (connected by a switch so it could be switched out). Actually from the top leg of the volume POT to the wiper. Something in the 100 to 250 pF range. That would boost the highs without lowering the output impedance, at least when the volume control isn't at the max.
fastcar1232 years ago
January 1st 2012. For some reason it won't let me copy any links right now.

The only difference is I deleted the jack (including the resistor on the input) and p1. I also grounded everything to one place on pin 5. The sound works when the circuit is off but when it's on I get no sound output
gmoon (author)  fastcar1232 years ago
Did it work before you deleted the volume control? Or were you still trying to get it functional? But you were trying to build something similar to this, right? But with a different tube I think...

As far as the Valvecaster, you should probably go to one of the forums posts where it's covered in depth. Lots of examples and pics there. They can offer more help than me. Remember, I've never even built one...
I was really wanting to get this to work with just one tube but It looks like if I'm going to build the valve caster I'm going to have to order a new set of components.
I never had a volume control for several reasons but mostly just tto simplify it. I want to build a circuit similar to yours with a different tube yes.

I'll go there but I'm far from tube savvy I just know how to solder a circuit together
fastcar1232 years ago
fastcar1232 years ago
If you could tell me the values for all of the components for the pcb- less 1 tube design on bevis audio then I could build that one instead
fastcar1232 years ago
If you could tell me the values for all of the components for the pcb- less 1 tube design on bevis audio then I could build that one instead
fastcar1233 years ago
Would it be possible to build this exact circuit useing the "Valve Casters" 12UA7 tube?
if not what is the differance between the 2 circuits that make the the tube not interchangeable?
gmoon (author)  fastcar1233 years ago
You could make something very similar for the 12AU7, but not exactly. And there's no way to guarantee the results because the 12FQ8 is a different tube, with different internal geometry.

There are some similarities--both tubes can use pins 4 & 5 for 12V heaters. No changes there.

Both tubes contain two valves; the 12AU7 contains two normal triodes, the 12FQ8 is something else (but I'm still using it as two triodes). Still, each tube's pinouts are different enough to require changes:

--Dual plates for each valve (four total).
--A single, shared cathode for both valves (one total).

--One plate per valve (two total).
--One cathode per valve (two total).

To convert a 12AU7 to something similar:

Since the 'litzer simply ties both plates together on each valve, then the single plates of 12AU7 should substitute for the dual-plates wired together. It will simply require one plate per valve rather than two. One pin, rather than two.

Likewise, tie the two cathodes of the 12AU7 directly together. This will simulate the single, shared cathode. So the single cathode pin becomes two pins.

None of this will necessarily give you the same sound, though. Consider it an experiment (much like the ValveLiTzer was). Frankly, if you compare the two projects, they aren't that different (low voltage, dual triode amplifiers). Once you convert this project to use a standard triode tube, the schematic probably won't look that different from the ValveCaster...

(I'm not going to look up and compare the pin numbers of each tube; you can figure that out yourself from the datasheets...)
I notice the Valve Caster project calls for 2 tube in what looks like a sereis circuit, however VallveLitizer calls for 1. so in order to combine the 2 plates I would need something like this?
I have basicly no experiance with any sort of tube system so i am probably wrong with this diagram but i do want to try it but unfortunatly i wasnt able to get a hold of any 12FQ8's
gmoon (author)  fastcar1233 years ago
Both the tubes are "dual"--two valves in one glass envelope. Both projects use two stages of amplification--as you say, in series.

How you draw a tube in a schematic is up to the designer. Often the two valves inside a single tube are drawn far apart on the schematic. It's tougher to do that with the 12FQ8, because of the single cathode--hey, it's a strange tube! So it might be harder to see there are two stages in the ValveLiTzer, but they are there...

Here's a datasheet for the 12au7. Compare the drawing with the 12FQ8. Your schematic--and your wiring diagram (the image you edited is a wiring diagram, not a schematic), MUST use the pinouts of the 12AU7, 'cause that's the tube you're using. So start from scratch, the pins aren't ordered quite like the 12FQ8. There is some overlap of the pins between the two, though.

On the 12au7 datasheet, you can see the two cathodes are pins 3 and 8. Those need to be wired together.

So--can you find the two plates on the 12au7 drawing? Their (2) pins will replace the four pins on the 12FQ8.

(I want you to figure some of this out yourself. ;-)
can you send the link for that. for some reason my computer wont open it properly
gmoon (author)  fastcar1233 years ago
It's a PDF. Try a "right button" / "Save Link As".

The link itself:

Here's a scrn capture of the pinout. And the other tubes in that family (12ax7, 12at7, etc) share the same pinout.
ok let me try to decode this

1- annode pate 1guitar input? {hot})
2- no idea
3- cathode of plate 1 which should go to pin 6?
4- VDC +
5- Common cathode (ground)
6- annode of plate 2
7- no idea
8- cathode of plate 2 (output to guitar jack {hot})
9- no idea

so im not entirely sure about this but i might be somewhat getting the hang of it. let me know what you think about it?
gmoon (author)  fastcar1233 years ago
It's a start. The "codes" on each pin are a help. The tube is split internally in to the 1st and 2nd valves.


1) 2P -- 2nd Plate
2) 2G -- 2nd Grid
3) 2K -- 2nd Cathode
4) H -- Heater
5) H -- Heater
6) 1P -- 1st Plate
7) 1G -- 1st Grid
8) 1K -- 1st Cathode
9) HT -- Heater Tap (center of heater filament, for 6V operation)

The grids in a tube are the "control"--voltage change here varies the amount of electrons that fly from the cathode to the plate. The grid is like the base of a BJ transistor, or the gate of a mosfet. So a grid would generally be the "input" of a circuit.

(numbering "sides" (1st & 2nd) in the same order as the 12au7)

1) 2nd Plate A
2) 2nd Grid
3) 2nd Plate B
4) Heater
5) Heater
6) 1st Plate B
7) 1st Grid
8) 1st Plate A
9) Cathode

There's no HT (heater tap) on the 12FQ8. That's OK, we don't need it.

So keep the heater wiring, as-is. Substitute the single plates for the dual plates (use one instead of two pins per stage). Connect the cathodes together.

Notice that the grids are the same pins on each. And that at least one of the plates on each side of the 12FQ8 coincides with a plate on the 12AU7.

The cathode pins are completely different.
so if my understanding is correct the the wireing diagram for the 12AU7 tube should look something like this?
12AU7 tube Valve guitar design.jpg
gmoon (author)  fastcar1233 years ago
Getting close.

R1 and R2 are swapped. 47K to the grid, 1M to the GND.

You're missing a plate load resistor on stage two (R4 on the original schematic, 1Meg). So there should be a 1M resistor between the plate and V+, pins 6 and 4.

Pin 9 (HT) shouldn't be connected. Don't use it at all.

Beyond that, I don't see problems (doesn't mean they aren't there, I just don't see any ;-). Good luck--there are no guarantees here, but in theory you should get output...
alright. so ive removed the 9th pin compleatly, put in the resistor between the plates and swaped R1 and R2
how does this look to you?
12AU7 tube Valve guitar design.jpg
^ right here ^
gmoon (author)  fastcar1233 years ago
Looks OK to me. I might have missed something, though.

But so long as you keep the voltage below 12V you shouldn't be able to fry the tube, so mis-connections can be corrected.

(Just don't use or touch Pin 9 with power, or you CAN fry the filament--that's the filament center, so it becomes two 6V filaments rather than one 12V.)
ok ill keep you updated when i start the project
fastcar1232 years ago
I built the circuit according to my circuit I drew up earlier minus the volume potentiometer but when it is on I get no output. Any suggestions?
gmoon (author)  fastcar1232 years ago
Hey--I missed some of your posts, sorry. Do you have the circuit schematic posted anywhere?

Without seeing it, my first guess is that you might be missing some coupling capacitors between stages. Subsequent stages might be overwhelmed by DC offset without coupling caps.

Other than that, can you test the different stages (tube, SS, etc) separately? Did everything work before you added the tube?
fastcar1232 years ago
I plan to build this circuit for an amplifier internally on the preamp stage. if the tube isn't touching anything would it be able to take a bit of wear and tear? (jostled around, rides in the car in different sitting orientations, being dropped, etc.)
gmoon (author)  fastcar1232 years ago
Within reason, tubes are probably more robust than most people think. I'd be leery of dropping the effect, but if you use a tube socket equipped with a shield, that helps.

Some folks use draw pull handles to make tube guards, to prevent the tubes from being stomped. You can even build the effect with the tube mounted inside the box; just have some decent ventilation holes...
Actually I thought that this project would be perfect for an amplifier I'm building. I would just mount the tube internally on some sort or metal raised platform as for ventilation, what would decent ventilation for a wooden box that's about the size of a normal amplifier head?
gmoon (author)  fastcar1232 years ago
For a wooden head cab, I'd make sure the tube socket was mounted on something metal, of decent size to sink away some heat, and then have ventilation holes above and below the tube. The holes wouldn't need to be huge, just big enough so air flows out from the top, and in on the bottom.

In a normal sized amp head, you should have plenty of room to mount the other components away from any hot spots.

Peavey had a whole line of amp (called PAG, "Parallel Axis Geometry") including the Triumph and the Bravo where all the tubes mounted inside the chassis. They needed a fan to keep it cool, but IMO it worked very well (I own a Bravo that was converted to a head).
upon opening my amp head I realized that when I made it I didn't plan for there to be any extra room needed so I have wires and PC boards scattered about inside it. so I wondered what would happen if I mounted it on the side inside the head rather than on the base or if I mounted it on the inside of the top piece. does the orientation effect lifespan, sound, heat variance, and the ability to change the tube out if needed
I plan to mount it on a square u-shaped piece of stainless steel that is raised above the wood about 2 inches
The amp head is actually already built at this point but I put a reverb pedal in it that I would rather trade out for tube overdrive. Could I just mount a fan on the back and have it connected to the same 9v walwart power source?
I can mount it on the opposite side of the transformers
Just getting started building some solid-state amps -- but this looks way cool. I'm ordering parts and want to get a decent regulated 12v adaptor. Does anyone have any data on average current draw ? Thanks
gmoon (author)  SleepySamSlim2 years ago
Should be approx 180mA @ 12V...
jgafford3 years ago
Finished making V0.4 earlier today, still got a lot of hum but it's tolerable. I'll put up some pics in a few days.
I'd like to label the pots, but not sure what the correct terms would be. Gain, bias, volume, tone..etc?
gmoon (author)  jgafford3 years ago
Cool, hope you like it.

It's pretty much Gain, Volume and Bias (which is very subtle, but interacts with the gain).

If you don't have a quiet power supply, you might add the Huminator from Beavis Audio, as Jon suggests below...
jgafford gmoon3 years ago
I'm already using a regulated power supply set to 12v, but the huminator sounds like a good idea. And I was more asking which pot did which function.
gmoon (author)  jgafford3 years ago
OK-- I can give you greater detail about the controls:

The Volume is just a post-effect voltage divider. Pretty much a standard volume control.

Gain is a POT through which the cathode is connected to a bypass capacitor. More capacitance here boosts gain (and bass).

The Bias control sets the amount of bias (voltage offset) on the tube. It probably changes the effect the least. But it can change the overall sound character. Because the bias resistor (POT) itself is what the gain control "bypasses," there is interaction between the bias and gain controls...
jgafford gmoon3 years ago
I'm one knob short cause that pot was bigger than the others... my bad. Tube also has a shield which didn't make it into the photos.
gmoon (author)  jgafford3 years ago
Hey, looks great! I like that type of tube socket that takes the twist-on shield. Easiest way to protect the tube I know of...

The Huminator should help.

Otherwise, I don't see a reservoir cap (the Huminator has one, so no need to do both).

If those don't fix the hum, look for ground loops. Sometimes "double grounding" the jacks is one such loop--including ground wires, when there's already a ground path through the chassis...
Out of curiosity, is it the resisters or the capacitors that affect the tone? As in which would I swap to alter the tone (if that makes sense).
gmoon (author)  Fender Fanatic3 years ago
In a very real sense, everything in the circuit can affect the tone...

The type of tube, the plate voltage, the length and position of wires, etc. So the plate resistors (R3, R4) affect the plate voltage. As does the overall power supply voltage--which mustn't exceed 13V or the filament will burn out. But two supplies can be used, one for the filament, one for the actual circuit.

And certainly both the caps and resistors have an effect. The circuit utilizes "capacitive coupling," in which the cap / resistor pairs form a high-pass filter, the response of which can be altered.

And the bypass cap and POT, together with the bias POT affect the sound, too.
jgafford3 years ago
what other ways are there to protect the Tube?
What kind of switch would you suggest for your V0.4 Valvelitzer?
gmoon (author)  jgafford3 years ago
Most people just build a little protective frame around the tube, usually with drawer pulls or u-bolts. Some place the tube inside the case (needs lots of vents, though). A tube socket with a detachable aluminum shield does a decent job, too.

I'm a little embarrassed I never built a more presentable one after the prototype (which I still tweak from time-to-time).

Stompswitch? I'd use a DPDT or a 3PDT footswitch. Something like this. A 3PDT gives the option of adding an LED indicator...
Luigi_xp3 years ago
Do I can use the 12UA7 valve?
gmoon (author)  Luigi_xp3 years ago
Did you mean 12AU7? See the link for the "ValveCaster" on page 2-- that project uses a 12AU7...
ptoadpipe3 years ago
Love the design and you use of "odd ball" tubes! I've been working on a small "tube-state" amp that uses 2 6AV6 tubes at low voltage, but I'm not getting that kind of warmth I'm hearing out of this guy. So I've got a few questions.

With my setup I'm using 2 supply voltages, 6volt for the filaments and 40volt for everything else (my "power stage" uses 40volt also, but is opamp). Have you tried upping the voltage on your design? If so, what was the outcome?

Your gain control (ver 4) adjusts bias, which is something I've never seen before but I find nifty. In my design my gain control increases/decreases the output from the first triode into the second with a baxandall eq tossed in for good measure. Oh right, the question... Ever tried that sort of a setup? The bias adjust would be fun to play with on mine, but having 2 cathodes might make it tricky.

Would love to read you thoughts on this!
gmoon (author)  ptoadpipe3 years ago

Thanks! The newer schematic (with the larger bypass cap) has a LOT more gain than the video.

Nope, I've never tried a higher plate voltage. At one point I drew up schematic with two separate V regulators (one fixed for filaments and one adjustable for the plate) w/filter caps all on the same board as the effect, but I never actually built it...

Yeah, the bias control I just stole from the "valvecaster," and the gain control is sort of an adjustable cathode bypass--but that's pretty common in solid state fuzz boxes.

Having separate cathodes is probably good--more options. Separate POTs or even trim pots could work there. I've been thinking about eliminating the bias POT and just having a HI/LO switch, since the gain control has more effect. But you never know that stuff until you live with effect for a while...

A more traditional tube gain control is fine. Although you see those more on amps where you have three or four tubes in the preamp stage. Only testing will tell. I've never used a baxandall, but I've played with some active filtering on other projects. If it's a true baxandall it uses negative feedback, right? You'll probably see more attenuation of the signal as a result. Let me know how that's working... I should probably at least add a simple hi-cut tone control to mine.

I did try using my ValveLitzer as the amplification part of my variable-inductor wah...which is configured as a negative feedback active filter. But the low-voltage tube doesn't have enough gain to recover the signal to a usable level.

Rock on...
smash101013 years ago
OK, so first off, nice 'ible, I'm going to make something like it if i can. now for the questions:
I just got 3 RCA 26 tubes, 1 RCA 27 tube, 1 RCA 71A tube and 1 ER 226 tube, can I use any of these for something similar? I know next to nothing about tubes in terms of how to use them in this (or any) type of project
gmoon (author)  smash101013 years ago
Thanks! Unfortunately, it's hard to predict how any tube in low-voltage "starved plate" mode will sound. The only way is to actually build it! About all I can tell you is that those tubes are fairly old, even for tubes.

Triode circuits are fairly simple. However, most of those tubes are single triodes (not sure about the ER 226, couldn't find it), and generally this type of project uses dual triodes. Using two would increase the complexity and the current requirements...
I'm pretty sure the er 226 is just a different brand of the rca 26, and yeah, they are very old, i got them off a radio from the 1930s, I don't even know if the tubes still work. basically i want to build one probs with the 26s because i have replacements for them, but i don't really know where to start with designing the circuit or even how to tell which pins are which.
gmoon (author)  smash101013 years ago
Just look up the tube datasheets on a site like this one. The pinouts will be there (generally drawn from a bottom orientation).

Triodes are pretty simple, probably easier than understanding transistors. Here's a decent introduction.

Study my project, and the Valvecaster (link is in my ible) which is "normal" triodes. Both of these projects use dual tubes, so you'll need to use two of your triodes to match the gain/effect of one dual tube.

Buy some sockets (ebay, Antique Electronic Supply, etc), or "recycle" them from old equipment. Also-the supply voltage for these projects doesn't exceed the filament (heater) voltage--that would fry the tube.

The datasheet will show the filament voltage for each tube, as well as the current draw...
jon pruett4 years ago
This is a great little circuit! I built two of them over the last couple days and really love the sound. I used the version 4 scematics with gain and bias pots, and two different 12 volt power supplies.

The first power supply came from eBay and was intended for a 12 volt security camera. It's a bit of a squeeze in the box, and add a good bit of hum when used with a single coil pickup. But all is not lost - with a pizeo pickup in a cigar box guitar there is no hum at all and this thing rocks!

The second power supply went to a dead netgear router - I salvaged the connector too. This one has almost no hum at all, even using single coil pickups. Love it!

Here's a couple videos - these are defiantly worth building!


gmoon (author)  jon pruett4 years ago
Hey, those look great! Love the guitars, too..and everything is built from cigar boxes--that's a nice touch.

You can dial in more gain than the videos, right? You've got them set for the more "natural" sound, I suspect.

I ask because I need to make a follow-up for this project (something nicer than the original prototype), and I'm thinking of a few changes. For instance, the bias knob could be replaced with a hi/low bias switch...
Yep - the gain can be dialed up a good bit more - I've been balancing the gain and bias knobs to get a warm tone with just a little distortion up at the top. I agree that the bias knob would be a good candidate for replacing with a switch - it can be confusing to use with the gain. Also, the overall circuit doesn't seem to shape the treble sounds nearly as much as the bass and mid range - is there a way to get some of that warmth into the higher octaves?

Thanks for a very cool instructable!
gmoon (author)  jon pruett4 years ago
Cool, thanks for the feedback.

Something, maybe a switched trim-pot might be good for the bias.

A couple ways to boost the treble:

-- change one or both of the coupling caps from 0.01 uF to a smaller value--like 0.0068 or 0.0047 uF. That would cut some of the bass. There would be some overall attenuation to the effect volume, however.

-- bridge the volume POT from the signal side to the wiper with a small cap, something like 470 pf or 330 pF. This could be "switchable," too, as a bright-switch.

I'd also like to add a simple treble-cut tone control. When the device is cranked to the maximum, there's too much treble for my taste.
Built my 3rd one of these last week! I gave my first one away as a present and a week later was asked to build #3 as a matching set with a 1/2 watt amp.   I hard wired the bias with a 100 ohm resistor and just put the gain and tone pots accessible to the player. 

I used a reclaimed 12 volt power supply from a cheap and busted printer and had huge humming problems even though I shielded all of the inside box surfaces with conductive tape.  But all was not lost!  I took an idea from the Beavis Audio "Humminator" circuit and attached a 100 ohm resistor, 100uf cap, and .047uf cap in the power path and it sounded crystal clear!  Very happy that three simple parts eliminated the mains 60 cycle hum interference - that might be worth adding in to future versions of the schematic so others don't have that same pain. :)


gmoon (author)  jon pruett3 years ago
Nice work, Jon--as usual!

I'm glad the circuit is working well for your setup.

Yes, any type of RC power filter (like the Humminator) will aid in reducing the hum--an LC filter (choke) might work even better. Since it's (the Beavis Audio circuit) somewhat less complicated than a regulator, it's a nice option.
Ahh - *** {lots of wikipedia reading} *** it's all starting to make more sense now! The math looks a little daunting on sizing some of the different choke or inductance parts, but now I know more about what those little buggers are used for and generally how they work.

ahh wired it up but i don think its working right. im getting very little volume and a lot of hum. i checked my wiring to the diagram. (the two pot version with the true bypass switch) pretty much the only part that isnt new is the volume pot. any ideas? thanks
gmoon (author)  SteinerChild4 years ago
Simple debugging first:
-- Double-check the wiring.
-- Does the bypass work correctly?
-- Make sure there are no cold solder joints.

Hum is discussed in the ible, and in many of the posts. All these low-voltage tube projects are very susceptible to hum, so they MUST be in a shielded metal box and ideally should have a regulated power supply...

Check back if those suggestions don't help...
anyone needed 12FQ8 tubes I have about 56 of them at 2.00/ea plus shipping
send me an email at mdonmyers@yahoo.com
I finished mine and had a great time building it.  It's the first project that worked the first time I tried it, on the breadboard and in the enclosure.

It does get a little hum, though.  As a consequence, it comes through a little muffled.  I didn't try eliminating it on the breadboard because a) I figured the enclosure would shield the circuit from the interference that was causing it and b) I wouldn't really know what to try anyway.

I think it sounds best when I play with my fingers.  It definitely convinces as a bluesy overdrive.  It was a lot of fun to build and it's a lot of fun to play.  Here's a sample of it:

gmoon (author)  flagrantfouler4 years ago
Glad your diggin it. Unfortunately, "page not available" on your link...

90% of the noise associated with this project comes from power supply issues. You can always try a fresh 9V battery, and if the noise is gone--it's the PS.

I see from your grounding question that your power supply voltage is 14V before regulation. Some regulators (7812) need more "headroom" from the input voltage, at least 15 to 16V. Otherwise they won't work right and be noisy. An LDO (low drop out) regulator will work for 14V to 12V, though...
Hmm I didn't know that. Good detective work!
gmoon (author)  flagrantfouler4 years ago
Ja. 'Course if it's still on a breadboard and not in a shielded box, that's a problem, too...
does it need any sort of earth? probly stupid but cant see one on the diagrams
gmoon (author)  SteinerChild4 years ago
There is a common ground, of course. It's pretty clear on the schematic, but maybe not as obvious on the wiring diagram (everything is "star grounded" on pin 5).

But you're probably asking about an "earth" ground reference, right? Like most stompboxes, this is low-voltage and doesn't really require one for safety--for itself, anyway.

But the ground is directly connected throughout the circuit, so if the amplifier ground is "earth", then that reference is passed by the ValveLiTzer from the output jack straight through to the input jack...
bishopdante4 years ago
whoa, freaky!

I like where you're coming from, I've heard of underbiasing, but this sounds really exciting.

What happens... if you don't give the valve a constant voltage... but instead feed it... a signal?


You should so put an audio sample up onto something like youtube so that ppl can hear the results (of your existing one).

Keep up the good work, dude!
gmoon (author)  bishopdante4 years ago
Thanks! There's an old vid on the first step, but with the larger bypass cap this has a LOT more gain currently.

Like a "cascode" or similar? I have no idea...

This particular valve has the cathodes tied together internally, so it's a little difficult to set something like that up with just a single tube.
any clues on how to wire it with a 6-pin DPDT button?
dint have a 3 pin one at the shop
gmoon (author)  SteinerChild4 years ago
Does this help? --True bypass link

The difference is that the valvelitzer drawing only switches on the output side. It leaves the connected to the tube grid when "bypassed."

If that's not clear, I could probably draw a second "true bypassed" valvelitzer diagram.
that would be really awsome if you could be bothered hanks a heap for the advice
gmoon (author)  SteinerChild4 years ago
I added a new step (now step 5) with the updated wiring diagram.

I think it's OK, but it's not verified. ;-) Good luck, have fun. Any questions--ask.
so you can bump up the capacitors and resistors like to says to get more HECTIC FUZZ ye? sicko
gmoon (author)  SteinerChild4 years ago
It doesn't quite get to the "full-blown fuzz" effect level, but there is a lot more gain if you use the larger bypass capacitor...
How do i convert it for 12AX7 ? ;) ( it costs me only $6.50 )
My town doesn't have an oddball tube such as 12FQ8 , only NOS ones . ( that costs me 50$ SGD !!! )
I have some 12fq8 tubes
Where are you located?

I would like to build one of these as well.
But don't need all these 12fq8s
SG , yeah .
What is SG?
are you saying you would like some of these tubes?
I can test out a couple and send them your way.
I have about 20 that are stamped Wurlitzer just like the picture above.
Singapore ._.
gmoon (author)  Thereyouhaveit4 years ago
You could try building the "Valve Caster" instead (the link is above in Step 1), 'cause that's already designed for the 12ax7...

(actually, AES (tubesandmore.com) sells the 12fq8 for $5.50)
I searched for some time , i still can't find a FET version of this , any ideas ?
gmoon (author)  Thereyouhaveit4 years ago
For this specific tube? I doubt there's an exact FET analog.

But the double plates (anodes) of each side are simply tied together on the outside, so its probably just acting like a single plate. I imagine that's not very different than a single FET "drain."

Both sides share a single cathode, so tying the "source" pins together (before any biasing) on two FETs would be pretty close... Maybe. Worth a try.
Actually , i was trying to say , a FET version of this booster .
gmoon (author)  Thereyouhaveit4 years ago
Ahh. I guess yours will be the first ;-).
Jhmdean4 years ago
Jhmdean says:
Ohh crap. After bench testing I started to mounting the components into a case. When I fired it up I realized the tube wasn't glowing. So i decided to test if it was recieving power. Lo and behold my 9v 650 ma adapter was putting out anywhere between 12 and14 v.

I can safely guess on of my valves is written off?
gmoon (author)  Jhmdean4 years ago
If it hit 14V, possibly.

Otherwise, just test the filament with jumpers and a good 9V battery. You should see the glow, if the tube is good.

Unregulated supplies depend on the load to drop the voltage to the "correct value." If the load is smaller, the voltage probably will be higher...
Jhmdean gmoon4 years ago
Yeah the load thing. I was testing it initially while running then I yanked it out and tested it just with the multimeter so no wonder it was running14v. Anyway all enclosed and pumping tube was fine, just a little short circuiting with my components. Awesome project gmoon thanks for the help.
gmoon (author)  Jhmdean4 years ago
Thanks! Rock on...
Nice instructable, I'll be doing this one soon :D
So what values would you suggest for the purest sound, as to use this only to 'tube' my sound up a bit? Also, reckon I could use this as a headphone amp? Might be cool...
gmoon (author)  Radioactive_Legos4 years ago
Haven't tried this as a headphone amp. It was never "scoped," and I don't know the total gain. It's above unity gain (hence the output volume pot), but it may not be enough to drive headphones.

That said, it might work. With 13V, at the max volume, max gain setting, it really boosts amp output.

The gain and bias adjustments can dial in a lower gain, more natural "tubey" sound. Everyone's preferences are different...
capth00k5 years ago
Thanks Gmoon, it worked for me. Tube distortion is OK ; but I only have a wall adapter (unregulated power supply) so a constant hum is present. Would there be a way to turn distortion / gain completely off and just use this as a tube preamp?
gmoon (author)  capth00k5 years ago
Glad it worked for you (though enough people have built it that there's no doubt the circuit works.)

If the gain control (last step) and volume control don't adjust the gain down enough, you can reduce the values of the plate resistors (R3 and R4). Dropping them will lessen the gain...
capth00k gmoon4 years ago
Thanks again gmoon. Great write up, I learned a lot in the process. Here's a couple of pics. I also used sockets for two of the caps, so I can change those capacitors to experiment with different tones. I'll try the R3 / R4 resistor trick . Might be the ticket.
gmoon (author)  capth00k4 years ago
Looks wicked cool. Thanks for the kudos--rock on.
Jhmdean5 years ago
Awesome got this beast running! At the moment I am running a double pole switch as a single (just one side), when my signal is bypassed i get a great clean sound with a really faint low volume distortion underneath it. I got my flatmate to check it wasn't just me :) Is this the case with everyone or perhaps my components. Is there a way I can true bypass? Does the tube need a load all the time? Any suggestions would be awesome.
gmoon (author)  Jhmdean5 years ago

I don't know why you'd get a distorted signal when bypassed. Best guess would be to check if there's a cold solder joint somewhere.

But yeah, you can "true bypass" it, and still leave the input pad (resistors) in place. They probably wouldn't matter anyway when bypassed. That would hopefully solve your problem. You might even be able to use your existing switch (if it's DPDT.)
Jhmdean gmoon5 years ago
Cool thanks! I'll have a nosey this weekend and try to find a cold solder. Else will enquire about true bypass. :)
bcraun5 years ago
Exactly how bright should the filaments glow? I've built most of the circuit and when I use a 9V for supply, it glows just a little bit. I used a multimeter to check V at various places and most of them are in the 8V range depending on where it's tested. I haven't been able to get the jacks hooked up correctly or the switch yet, but am curious if the filaments are supposed to be bright. If they are, then I've got a problem. Thanks for your (continued) help.
gmoon (author)  bcraun5 years ago
Good question--the filament glow isn't very bright at all.

The glow looks bright in the photographs 'cause I took 'em in low light and used a tripod. Longer "time exposures." in other words...
bcraun5 years ago
I located a bulk film can. Do you happen to have an electronic version of your drilling template?
gmoon (author)  bcraun5 years ago
AAAAHH! It's just a slap-dash prototype! I never expected anyone to want to copy the case.

Seriously, I accidentally swapped the right-left orientation of the input-output jacks, and they are backwards from the "normal" In/Out orientation. You don't want to copy me...

(If you do use the film can--they are kinda fragile, so support the can well when you drill, or it'll bend in on ya...)
bcraun5 years ago
Hi, love this instructable. My question concerns the SPST ON/ON footswitch. The one I purchased from AES was listed with the same specs as you did, but it only has 2 terminals. I can't seem to find an equivalent switch that is SPST ON/ON with the 3 terminals as shown in the pictures and wiring diagram. Is it possible to use the one I have or so you have a source where they can be purchased? Thanks, -bill
bcraun bcraun5 years ago
Actually, now that I have looked a bit closer, this appears to be a SPDT switch which would have 3 terminals. Need confirmation though, thanks.
gmoon (author)  bcraun5 years ago
Which switch from AES did you buy? I see that many of those are "momentary", which won't work...

You don't preciously need a three terminal switch for this project, it's just the minimum. AES sells other switches (like the P-H501, 9 pins) which would work well. That one in particular could be used for "true bypass", and even add an LED indicator lamp...

AES is a quality shop, might as well buy there as anywhere...
bcraun gmoon5 years ago
It's the P-H493 (Carling SPST). I thought it was a pretty generic switch. Looks to be a simple ON/OFF type. I believe what I'm after is a 3-terminal SPDT though, right? I would need a bit of help with the wiring on any of the other terminal combinations. Thanks for your patience.
gmoon (author)  bcraun5 years ago
Yep, the H493 is only SPST, and the type I used is SPDT.

A DPDT footswitch would allow "true bypass," (example) if that matters to you (hint: it might make a difference in an effects chain; or it might not.)

Here's a wiring diagram (halfway down the page)for the 9 pin 3PDT switches, like the P-H501 including the LED.

A 3PDT is just three SPDT switches in a single package--or one DPDT and one SPDT in a single package, which is how it's used (a DPDT is two separate SPDT switches in one.)
gmoon (author)  gmoon5 years ago
OK, ignore that "wiring diagram" link for a 3PDT--it's specific for a "cascaded" series of bypasses.

Check this out instead. It's a little more complicated, only because it also includes a power jack, and uses a 3-terminal TRS jack as a power on/off switch too (pull the input plug out and the power is cut--saves batteries).
Hmmm, okay I'm not getting it. I think I have something wired incorrectly. This is a beginner tube question, but should the tube heat up with supply voltage on pins 4 & 5? If not it is possible to wire it to test its functionality? I'm using a lab bench power supply and have built it on a breadboard and if i push c1 into r5 I'll get a rise in current (from .01 to ~.20) and the elements will start to heat. Otherwise, unmolested, I have no heat, no sound, nada. I'm going to try and build it into an enclosure and see if that solves the wiring issue. Thanks for the great instructable!
gmoon (author)  madeintaiwan5 years ago
Thanks! Yes, the tube filaments will heat up if only pins 4 and 5 are connected to power.

You probably have a short somewhere. Hopefully something simple.
Okay, with 4 & 5 connected, no warmy. With 4, 5, and *8* (which has the leg connected to 6) it gets warm....Is this a socket issue? Wiring? Have you tested how much power yours draws? I'm at 12.9v and .16a. 2 watts about right...
gmoon (author)  madeintaiwan5 years ago
The datasheet shows .15A @12.6V, so the current draw is correct.

The socket in the wiring diagram is viewed from the bottom, so be sure that's correct (if it's flipped, then what you think is pins 4 & 5 is actually 5 & 6).

(You're sure it's a 12FQ8, right? Several people have commented they built it with a 12AX7, which clearly ain't gonna work...totally different wiring for that one ;-)
12FQ8, unless someone is playing an elaborate private joke on me.... Damn you Wookie! Does the image below represent the correct pin numbers? thanks for the help.
gmoon (author)  madeintaiwan5 years ago
hehe...sorry, I had to ask, 'cause a few people had tried the other tube. Yes, that's the correct pinout.
I built pretty closely based on this schematic (I did a ton of research on my own to build a similar pedal before I found this!). I'm running on a 9V battery, so it takes a little for the filament to heat up. Anyways, while I was still at my bench, I ran a signal generator through the pedal into an old SS combo amp and it passed the signal fine, engaged and bypassed. When I took it up to my music space and put it between my guitar and Marshall, I can't get any signal through. I've double checked all the connections, but it seems as if something just isn't working. I've tried a few tubes (I actually had a Wurlitzer 4150 exactly like yours) and know the leads I'm using are good. Any thoughts?
gmoon (author)  Mightymatt545 years ago
That's a puzzler. Did you try again with the SS amp and substitute the guitar for the signal gen? Maybe it's something simple you missed. If it doesn't work with the original setup, possibly a cold solder joint or something similar. For whatever reason (input impedance, probably), I've found this circuit produces a little more gain from tube amps than from SS amps.
Jhmdean5 years ago
Yus found 2 down here in new Zealand! Has anyone made the version with the gain control?
gmoon (author)  Jhmdean5 years ago
It works for me. In all honestly, the bias POT could probably be replaced with a trim POT or maybe even a fixed resistor...
Jhmdean gmoon5 years ago
Well being my first tubey build I'll stick with the instructions! Reduce the rick of newby mistakes. :)
la-main5 years ago
Hi mine does not work correctly the tube glows and i can hear the sound with switch on, but there is a terrible buzz in the sound. If i adjust the pot i hear the weirdest sounds (really weird)  I made some pictures:
WOO dat case looks nice XD i could retry to fix it
gmoon (author)  la-main5 years ago
What is your power source--regulated or unregulated wall-wart?

Have you tried it with batteries, just to check if there's any power supply ripple?

Noise can come from many sources--cold solder joints, wire routing, a misconnection, etc. The weird noise might be oscillation cause by long lead dress, but check the power supply first.

Thanks for posting the photos (it would be difficult to trace the circuit with all that wiring, but it's helpful none-the-less.)
DefLegend5 years ago
Could I use a mesa boogie 12ax7 tube instead of the 12fq8 you use?
gmoon (author)  DefLegend5 years ago
No really. Read Step 1, and try the "Valvecaster" instead. Which may or may not work well with a 12AX7--it usually uses a 12AU7 instead, but at least those two tubes share the same pinouts...
fastcar1235 years ago
what exactly is that tool because i need one but dont know what to look for
gmoon (author)  fastcar1235 years ago
You mean the "step drill bit?"

Check out Harbor Freight...
awsome thanks
jake_ster25 years ago
Exactly what compasitors will we be using? Can I get exact specifications on each one? PlzKThx
gmoon (author)  jake_ster25 years ago
Sorry, mate, I never did make an official "parts list." But there's only three caps in the whole project.

Use the schematic on the last page, it's got more gain than the first one.. There isn't a "wiring diagram" for the changes, but they are small (one additional POT and capacitor) and won't be mounted on the tube socket anyway.

C1 and C2 are "film" caps--chose any type you want (mylar, polypro, etc.) They should be rated at 25V or higher.

C3 will be an electrolytic cap, also 25V.
 is there any specific tolerance? eg. -10, +50% or -20, +80%
gmoon (author)  jake_ster25 years ago
Those are electrolytic tolerances, right? I'd expect the film cap numbers to be symmetrical, but 20 or 30% should still be OK for those.

A closer tolerance for the electrolytic might be better, but it probably doesn't matter. In fact, you could substitute anything in the range of 20uF to 250uF for C3.

A higher value will give more bass response (and to some extent, gain)--up to a point. I didn't test anything larger than 100uF. And 100uF is definitely higher-gain than 20uF (or the original value, which was quite small.)
fastcar1235 years ago
so what tubes other than the 12FQ8 tube?
I ask because it is very hard to buy anything off the internet for me
so i know i have my crazy ideas but what i want to do i limit my number of chords and space use by them and the pedal

so what i want to do is intigrade this into the back of my amp ( there is alot of extra space back there)

now here are my problems
- move my amp quite often (in the car/truck/garage/etc.) so it has to be very tough but also not a fire hazard

-i have separate amps one ontop of the other which means i will need the device to be in one amp while haveing the ability to to feed signal to both amps from one guitar and at most 2 chords

-i have no free outlets anywhere so i cant ac adapter it but i also dont have the money to buy a 4-pack of 9Vs every week so does it use alot of power?

-i still want the ability to turn it off and on easily and to adjust the controls easily

so taking all these factors into thought how possible would this be
sorry about the long question
gmoon (author)  fastcar1235 years ago
If you cannot find this tube, you should instead consider the "Valvecaster" project--the link is on Step One, above. It uses a more common 12AU7 tube, which you should be able to buy at any decent music store.

You have lots of "requirements." Ultimately, I'm not sure one stompbox can solve everyone's guitar issues. I'd try playing with other off-the-shelf FX boxes before committing hours and hours to one complex build...

I can help you a little, but how successful you are will depend on the implementation details, because you may introduce noise with all that routing complexity. And even experienced builders encounter noise issues with their projects...

-- If you don't have any outlets to spare, you could tap the AC line inside the amp, and attach a wallwart internally. The project itself uses more current than a typical transistorized effect--tubes have a filament, so it's like a small light bulb.

Have you simply considered using a computer "powerstrip" to increase the number of outlets?

-- You should use a relay to switch the effect ON/OFF, instead of a normal bypass switch. That would give you the use of a remote external footswitch. The footswitch would activate the relay. Without the relay the signal would have to be routed a long distance--which would guarantee noise.

A 12V relay could use the same 12V power supply as the tube. There may be some transient switching noise.

But the controls--gain, etc., would still need to mounted very near the "guts" of the effect, for the same reason. Routing those signal lines more than an extra inch or two is begging for a noisy outcome.

-- No promises about plugging two amps into the output. Amplifiers have an input impedance (which is different from amp-to-amp) and two amps together would sum the impedance.

This might have minimal effect; or it might have a major effect. You won't know until you try it.

ok so i have some questions

1 wat is a wal wart? thats like an AC-DC adapter right?
2 i have a splitter that runs like this guitar------>splitter--->amp1--->amp2 and it seems to do just fine one amp is a bass amp and the other a guitar amp (i dont know if the amp type wolud have anything to do with the impeadance)
3 i heard from somewhere that powerstips can overload and cause a fire or electric shock when used with any thing that might add up to be higher than x number of whatts
4 the tube that you suggested as an alternative is this tube a high voltage tube or is it like this one that only puts out low voltage because im new at this and dont want to screw with voltage that can kill me just yet

gmoon (author)  fastcar1235 years ago
1) Yeah, that's exactly it. Some are too noisy for this project.  The other project will also have lots of info on power supplies.

2) It will just vary with the amp. Maybe your two amps can work with a passive splitter--it is "passive," right? Because an active splitter (powered) would probably work just fine.

3) I'm sure you can overload some powerstrips, but what's the total wattage of your amps? Unless the amps are large, they won't draw more current than an average computer.

If the amps are over 50 watts of output power, then they'll start drawing some serious total wattage.

4) It's a low-voltage project like this one. Both projects use tubes designed for "high voltage," but the tubes are used at way lower-than-intended voltage. It just happens to work with some tubes.
1 so just a regular ac adapter just mounted inside? wouldnt tha thump around if you moved the amp too much?
2yes just a simple y splitter
3they add up to be 54 watts together
4so at that low voltage the tube cant kill me. works for me!
gmoon (author)  fastcar1235 years ago
1) Yes, although unregulated adapters can be too noisy. If you "mounted" it somehow, then it wouldn't move, right?

The best type of adapter would be regulated, but switching regulators sometimes aren't "isolated," which can be dangerous. You can build a linear regulator with an LM317 for 5 or 10 bucks.

Whatever voltage / regulation / adapter you choose, it can't exceed the filament voltage, which max would be about 13V--or the tube heater will burn out.

There's more about powering the project on that "Valvecaster" link. It's a LONG thread, but worth the read.

2) OK

3) That's output wattage, or total? Anyway, you probably don't have more than 100 or 150 watts total, which is less than the average computer + monitor. That should be safe for any outlet or powerstrip.

Many powerstrips have a built-in circuit breaker anyway.

4) Yep.

1 would it be easier i just disassembled an adapter and uesd a metal bracket with a shield on it to secure it?
when you say regulated u mean one tha i cannot change voltages on such as an old router adapter (9.5 v)
3 yes one says 35 watt on the back and 17 on the other but if a power stip can do that with a computer then it sould be childs play for my amps
i only ask cus everyday i look at my 6 way spltter on another outlet and wonder how daguous it relly is to have 6 plugs filled

luudvig5 years ago
I found a "12AX7A" tube in my parts bin. Could I use this? Thanks
gmoon (author)  luudvig5 years ago
Wouldn't work with this project. You could try it with the "Valvecaster" (see the link on Step One), but I've heard that 12AX7 tubes don't work well there, either. The pin-out is correct, but they apparently don't work well at low voltage.

They do work well for high-voltage preamps like the Real Mctube. This project uses two wallwarts, back-to-back to provide 12V for the filaments, then boosts the voltage back up for the plate voltage (the two wallwarts also provide isolation, too.)

Be sure to use the older style wallwarts with transformers, not new switching wallwarts for that one...

Otherwise, this tube IS the most common preamp tube for guitar amps. You might just hold on to it.
yoda17635 years ago
 Nice guide, 5*. I have one question. Could you replace the phono jacks with rca jacks to use for home theaters or other uses, or would you need to do some additional modifications to do that? Anyway, good work. I would like to see more great guides from you.
gmoon (author)  yoda17635 years ago
Thanks, Y.

Hmmm. The input impedance of a stereo line-in is about 10K. That's quite a bit lower than a guitar amp. It would attenuate the signal somewhat, but it would still probably work.

It's not a "high-fidelity" effect, though. Personally, I think this would subtract clarity from a quality audio setup. 'Course I've never tried it...
gmoon (author)  gmoon5 years ago
On second thought--This probably has an output impedance in the 30K-60K range. That's pretty high for driving a 10K input impedance. I'm sure there would be some definite attenuation.

(Normally the output impedance of the preceding stage is 1/2 to 1/10 of the input impedance it's driving...)
therocksock5 years ago
i just built this and it doent work the onl differnt part i used from your list is the audio pot. it didnt look the same as the one you used
sorry i ment the linear was different
gmoon (author)  therocksock5 years ago
I don't know what to tell ya. It's been "verified" by several other builders. You've seen the updated schematic on the last page, too, right? (there's not wiring diagram for that, but it's a small change...)

Just check and double-check all the connections, component values, etc., including the tube (some folks were using the wrong tube!)

What does doesn't work mean? No sound? Sounds bad? Weak signal?
no sound comes through i have the right tube, the bypass works but nothing else
gmoon (author)  therocksock5 years ago
Then carefully check all the components and the wiring. The linear vs. log pot wouldn't prevent operation; it would just effect the adjustablity.

Does the tube filament glow? If not, there's a problem.

If the tube is good (no way to test that unless you have a second tube or a tester), then it sounds like a wiring problem--like maybe there's a connection to ground somewhere in the signal path.

If you have "guts" photos, post them here.
thanks i ll check the wirings. the filament did not glow
Davvik5 years ago
Hey guys, I have been slowly collecting all of the parts to create this project here;


That's the one mentioned in this instructable.  I was just wondering if it really mattered the type of capacitor I used.  I live in a small town and it's very hard to find Mylar capacitors, I can only get ceramic ones.
gmoon (author)  Davvik5 years ago
While you generally want to avoid ceramics in audio projects, they will work. Occasionally you'll see them used in tube amps, organs, etc.

They are just less linear than other film caps. If really accurate audio fidelity is the goal, that's not ideal. But if distortion is OK, they they'll be fine.
Davvik gmoon5 years ago
Well we are making a tube booster, are we not? I won't mind a little extra crunch to this project.
gmoon (author)  Davvik5 years ago
Exactly ;-)
plpicher5 years ago
gmoon (author)  plpicher5 years ago
Absolutely. Half-watt resistors are fine.
gtkid20026 years ago
Just curious, for a dual tube version, would you think it's safe to run each of the tubes off the power supply in parallel?
I answered my own question! I got dual tubes to work- BUT! I had to use a computer power supply to power it. 12v @ 3A. Don't know how it sounds, I just watched the tubes light up in five seconds though. Didn't run it for long, I don't trust my test connections. ... Might have blown the supply. I can't get it to turn back on. Go figure.
gmoon (author)  gtkid20026 years ago
I answered my own question! -- Yep! Running two off the same supply is fine.

The data sheet specs the current draw for one tube @ 12.6V as 0.15A. So two tubes together would draw about .3A--the discrete circuitry wouldn't add much to that, so the total draw would be less than .35A.

A 12V, 3A PS will supply the necessary current with plenty to spare...

Computer supplies sometimes need a load, or they won't function. If you tried turning it back on "bare," that could be the problem.
gtkid2002 gmoon5 years ago
I killed my own pedal! Hooking up the supply voltage backwards frys the tubes internals, excluding the heater anyways. Now I'm looking at a ten dollar dual tube nightlight. I'm so thrilled with myself. I can't get them to work, but I don't think it's a wiring problem. They're fried now, aren't they?
gmoon (author)  gtkid20025 years ago
I've "bricked" a few projects in my day, too.

It worked OK before you reversed the polarity, yes? If so, then new tubes are probably your only recourse. But have you checked any polarized caps? They'll burn out, too, if you reverse the PS.
gtkid2002 gmoon5 years ago
Yep. Checked all the caps and connections and the only thing I can think I did was fry them. But I get an awesome nightlight now, just have to figure out how to solder on these "non soldering" leads from the tubes.  

Pity, I never got the full dual tube pedal going. But I get some 12FQ8's and 12AU7's at the end of the week. I might try to make a cool combination of them and see how it sounds. Might even put a reverb tank in between tube stages to have something else to play with. 
gmoon (author)  gtkid20025 years ago
Solder the tubes? I must be missing something...sockets are the way to go.

Anyway, good luck with the rebuild.
gtkid2002 gmoon5 years ago
You're not missing anything. The tubes are fried, but the heaters still work. I just want to make a night light with them. I've always been a fan of glowing tubes.

I might post an instructable on what I'm doing, but I don't think it would be much help to anybody. I blew the preamp stage on my bass amp, so I'm building a new tube one, and I'm hopefully going to install it after Christmas.
gmoon (author)  gtkid20025 years ago
Ahhhh. I got it now. Don't see why that shouldn't be an instructable...
corbin5695 years ago

mine is making a really weird buzz when i turn it on and i can adjust the freq. of the buzz with the 50k pot, the only i things that i can can think of is my 500k pot dosent have a ground which is supposted to connected to pin 5
also i run it off a 9v battery, not sure if that has anything to do with it?!?! plz help thks

gmoon (author)  corbin5695 years ago
You should connect the other end of the POT to ground...it doesn't matter where you make the connection. Pin 5 (of the tube) is one side of the filaments, and doesn't constitute a ground in itself.

You can connect it to anything between 9 and 12VDC. I'd carefully check and re-check the wiring.

Does it function (can you hear the guitar?) with a buzz, or is the buzz all you can hear?
corbin569 gmoon5 years ago
no its just a weird sine wave buzz that i can control nothing from the guitar but the bypass signal works fine, could the tube be blown and make the buzz i did accidentally run about 3 volts through it backwards at first=/. also my pot is plastic so icant ground the case and it only has two pins
gmoon (author)  corbin5695 years ago
I doubt you could hurt the tube with 3V.

But when building tube projects, I always order more than one tube--sometimes you get a lemon.

Your sure it's the correct tube? At least two people have PMed me that it doesn't work with a 12AX7. Well, duh. They must not have read the whole project, 'cause that ain't the right tube...

A POT with only two pins? Are you sure it's a POT? In the design it's wired as a volume control. For it to function correctly, it needs to be a "voltage divider," and that requires a standard three-leg POT.

However, a volume control isn't absolutely necessary. You can simply omit it, and the effect will operate at max volume.

I encourage you to recheck the wiring, and your part values. Although I also like to use "creative substitution" for parts in my build, one bad or mistaken component can render any circuit useless.
corbin569 gmoon5 years ago
well i just found 27 12fq8 wurlitzer tubes on ebay for only 15 bucks=]=], couldn't pass that up, so when those come i should be good on tubes.  And for the pot issue idk i wasnt really sure if would work when i got it from radio shack thought it looked kinda weird with only 2 prongs, but it said on the package 500k volume pot, so i got. I ill prob just do what you said, and replace it with a 330k-1m ohm resistor. I,m not really paticular on volume level as long as i can still adjust the gain. thanks a lot for all the help=]
gmoon (author)  corbin5695 years ago
You're welcome--I'm sure you'll work it out. Good luck!
oh ya and the tube i,m using right now is 12fq8
gmoon (author)  gmoon5 years ago
Correction--omit the 500K POT, but replace it with a 470K resistor connected to the ground. Just about value 330K - 1 Meg will work.

The coupling cap together with a resistor (fixed or POT) form a high-pass filter.
addies5 years ago
Do you happen to have the tab for that little riff you played in your youtube video?
gmoon (author)  addies5 years ago
Seriously? It's just a "toss away" riff composed on the spot for the vid, and very simple. But what the heck-- it's so easy to tab, here it is:



It follows a typical I - IV - V progression, E - A - B.

You'll have to copy-and-paste this into an editor with fixed-width fonts (like notepad.) That will fix the formatting.  Instrucables doesn't let us "non-paying" members set the font anymore...

Antoto5 years ago
If I just add a speaker to the ValveLiTizer, will it do an amp?
gmoon (author)  Antoto5 years ago
Sorry, didn't see this before. Nope, the Valvelitzer doesn't provide enough gain to push a speaker. Never tried it with headphones.
could i adjust this somehow to use a 7 pin tube? it is a 6bh6 tube, and if it is possible to adjust it to use that tube... how would i do it. thanks a lot!
gmoon (author)  mikehayworth5 years ago
Hmmm. The 6bh6 is a pentode, which is quite a bit different than the dual triode in this project.

It's possible to build a similar device with a pentode, but I'm not sure there's any preexisting example for you to work from...

Search for "pentode preamp", look at some earlier guitar amp examples (early gibson, for instance) which used pentodes instead of triodes in the preamp. Here's an example of a modern project. Although most amps use pentodes in the power amp, that's not helpful to you here--those are current amplifiers, rather than voltage amps (instead of raising the signal voltage, they produce the current needed to push the speaker cone.)

About the only advice I can give is that low-voltage operation will require high values for the load resistor (between the plate and the B+ voltage) and higher values for the cathode resistor (between the cathode and the GND) to give it drive. But what those values might be ???

Pentodes have a different topology, so you need to account for the extra grids (screen and supressor grid) when designing the circuit.
How many miliamps does this pull? Could i run it off of a 9v 200ma wallwart?
gmoon (author)  lightsaber.guy5 years ago
The tube draws about 150 mA @ 12V. Not a lot more current is required.

Normally I'd recommend using at least a 300mA supply, but maybe with 9V the tube will draw less current and you'll be OK.

I'd recommend you hook it up and meter the current draw. I haven't had much luck with unregulated power supplies, though--too noisy.
jeff-o6 years ago
Are the pots logarithmic? I'm assuming yes...
Only the 500K pot is. The other one, the 50K gain pot, is linear.
thevadj5 years ago
I see this is mostly a guitar preamp, but it gave me an idea. How would this sound with normal music playing through it? Might be nice to have a tube pre-amp between my laptop & surround sound.
gmoon (author)  thevadj5 years ago
Hmm, yeah. That I don't know.

The original version of this doesn't distort too much, and even the updated schematic can be set for minimal distortion.

However, (and I'm not an audiophile) there would still be some distortion, due to the low-voltage operation. Whether some of it would be the more pleasant 2nd-order distortion that audiophiles like, I don't know. In general, gear designed for guitars doesn't work well for stereo use (except at low volumes.)

Maxed, I'm sure this generates a good amount of odd-order distortion that works so nice for guitars, but not for general audio.

These low-voltage experiments are "off the charts" as far as the original tube datasheets, and I certainly haven't done any of the complex testing necessary to figure accurate distortion data...
thevadj thevadj5 years ago
(Using a stereo version of course)
capth00k5 years ago
Thanks for the write up on this. Awesome stuff.
gmoon (author)  capth00k5 years ago
Thanks :-)
Hey I wanna first say that I think its awesome how patient you are and how willing you are to help. Next i have a question as to how it would be possible to make this pedal a 'true bypass'. Here's what I tried and i just wanted to ask if you think I got it right. It's not working right new because i soldered the power jack backwards. I know i could just re-check once i finished but i was still going to ask because i wasn't sure if this was actually true bypass or not. Thanks ahead of time Jordan
gmoon (author)  lightsaber.guy5 years ago
Hey, ls.g... Something strikes me wrong about that drawing--pin 5 is the common ground for everything. RE: "switched on"--The center of POT 1 should connect to the output. The input should connect to R1. Both the jacks also have a ground connection, too (but that doesn't need to be switched out.) The bypassed mode looks OK, though (input and output connected through the loop at the top.) That's assuming I'm reading the type of switch correctly, of course... Thanks, BTW. I enjoy all the feedback; helps make the projects better, too.
ok here's my updated switch but its still not working. I fixed the DC jack and i changed the layout so that all the negatives meet up w/o going to pin 5 and instead go directly to the negative plate on the DC jack. The tube still hasn't lit up and neither has the led. I don't think it my soldering but i redid all of the joints very carefully just to be sure. any advice is always appreciated.
gmoon (author)  lightsaber.guy5 years ago
If the tube isn't glowing, the problem isn't the bypass switch--bypass isn't a power switch. That's a separate issue. The power routing shouldn't go through the bypass--except to the LED, which is only an indicator of the bypass status, NOT an on/off lamp.

Try this:
        -------        |     | ---   ---   ---pin5  input  output (i & o on jacks)  |     |     | ---   ---   ---       R1    POT1 (center)        |     | ---   ---   ---  |  | LED (connected to V+ through resistor)

This is assuming your switch is a 3PDT bypass switch, in which the middle horizontal rail connects, when switched, to the top and bottom rails.
maxrussek5 years ago
I HAVE JUST BUILT THIS BUT its not working. the tube glows and i can hear buzz etc when you touch untouch the strings but no sound comes through the amp. i have used a 12at7 valve and have not used a foot switch just if its on its on. i also havent used the excact caps and resistors just close as i could get. any suggestions on what might be wrong
gmoon (author)  maxrussek5 years ago
This project uses a 12FQ8 tube, not a 12AT7. The pinout is different. No way would that tube work with this wiring. You're using a typical dual triode tube, which shares a pinout with other tubes like the 12AU7 and the 12AX7. Links to the "Valvecaster" project are on Step 1. I suggest you build that instead.
maxrussek gmoon5 years ago
aaaah thank you so if i get the same tube it should work for me? thanks, awesome
gmoon (author)  maxrussek5 years ago
It should, if everything else is setup correctly...
Wesley6666 years ago
I have a collection of vintage/antique tubes from between 1920 - 1965. Would any of these work for this project?
gmoon (author)  Wesley6666 years ago
Maybe. Unfortunately, this is a very odd-ball tube and I doubt a substitute would work. But if you have any 12V dual triodes, you could try the "valve caster" project--the link is provided on Step 1.
Wesley666 gmoon6 years ago
ok thx.
Hey, here is my finished work, thought you may like to see it:




It has amber LEDS underneath the valve and the case, so it gives a lovely glow when on, can't get a good picture of it in the dark though:http://www.facebook.com/photo.php?pid=3685297&l=88ea6fafb6&id=630911404

The 2 Meg pot replacing R3 and R4 is very cool, you can really change the sound from clean to mega distortion! I added a 9v battery lead inside the case (for emergency use!) I use it with the power supply though mainly. I can change that from 9v to 12v so there is quite a lot of variation I can get from it.

Thanks again for your help, nice project. Looking at some other 12v and 30v designs now amongst a LOT of other projects. This really gave me a lot of needed confidence, nice one.
gmoon (author)  planet sutcliffe6 years ago
Hey, that looks great! Really nice job on the case. (just got back from a two week vacation, or I would have seen it earlier...)
Thanks very much! The case is an ikea drawer which I cut down in height, used the excess to strengthen the box. The metal is 1MM alu sheet with hammerite paint. The tube guard is made from earth cable (thanks to the electrician for that one!) This also is my chassis ground as my other two materials are insulators. I did think about etching the alu but I would have had to choose a good stencil as it would not take long for the etchant to eat the whole 1mm. This could be a great effect though you would be limited to "stencil" fonts. Would look good with LEDs under too.
gmoon (author)  planet sutcliffe6 years ago
Etching might be cool... Anyway--job well done. Both your case and Jeff-o's put my prototype to shame in the "looks department..." Thanks for the comments, glad it works well for ya.
We couldn't have done it without the circuit though! Are you still working on the Valvlelitzer 2 by the way?
gmoon (author)  planet sutcliffe6 years ago
I won't work on a two-tube version for awhile--I'd like to build a "presentable" version of this one first, and too many other projects are half done: -- finish rebuilding my Ampeg Gemini II -- modding a Kalamazoo Bass 30 for guitar -- finishing my "true inductor wah" -- converting a small tube amp into a "herzog" -- adding an isolation trannie to a small Gregory amp -- build a 2X12 cabinet I'm sure there's other stuff I'm forgetting at the moment...
Sounds familiar! I now have a huge thirst for the DIY electronic audio biz; It has surprised me how much I have got into it so quickly actually, although I do have that in my character; it's all or nothing...
gmoon (author)  planet sutcliffe6 years ago
I hear ya....I'm actually a little more patient than when I was younger. I think some of the projects have benefited from that--not rushing in and trying to build something in a day. But I fully understand the "all or nothing" part. RE: too many projects--we visited my in-laws today, and I was given the gift of a 1930's Oahu square-neck acoustic lap-steel guitar, complete with it's original and unusual bottom-opening case. It needs a bit of work, there's a few cracks on the top. They found it at a yard sale, and paid (...wait for it...) $5. Sigh... I now have several guitars now that need work. But am I a happy boy? Yup!
Amazing! Well, I expect that has shuffled your guitar priorities around for you... I think all projects benefit from taking the work slowly and methodically, and if you have multiple projects going at the same time then you just switch to another if you need to wait for parts or inspiration. They all have transferrable skillsets too, so you can learn something on project A and apply it to project B. Without A, B could have been much more difficult to complete, or less effective when completed. I'm going to start making some analogue synth modules soon, some from schematics and some from purchased PCB's. I am going to finish up some more projects first, but I can't wait really! Should be fun fun fun, probably going to be a bit of a headache (the good kind) as well though.
gmoon (author)  planet sutcliffe6 years ago
Have fun with the synth modules! Nothin' like analog for sounds. I don't know if I'll plunge right in with the Oahu, or work on some of the other stuff...
I LOVE analogue sounds; I already have several oldschool a-synths; MS10, Juno 60, a Russian beast called an http://www.ruskeys.net/eng/base/ritm2.php. I really can't wait to make my own modular! Let me know how you get on with the Oahu, I'd like to see it; send me a pm or something.
fatfoohy6 years ago
could anybody send me a diagram of how to wire a tube if i was just to wire it with power and an input and output, basically just a tube, minus the knobs and resistors and capacitors and what-not
gmoon (author)  fatfoohy6 years ago
You're better off building the circuit with the POT controls. And most of the caps and resistors aren't "optional" -- correct operation depends on all the components being there.
fatfoohy gmoon6 years ago
hmmm, well what i was hoping to do was build a tube screamer pedal, and then just wire the tube in right after the effect, so how bout a diagram with only the bare necessities, like no pots
gmoon (author)  fatfoohy6 years ago
Looking at the new schematic on Step 9, for max gain you could eliminate P3, and connect C3 directly. P2 could probably be replaced with a 47K resistor (probably.)

You could also replace P1 (volume) with a 470K resistor, but without a volume pot, you'd probably be unable to "dime" your amp completely, so if it produces any decent distortion when cranked you'd loose that.

If you make those changes, the effect will be nonadjustable. You could replace those POTs with trim pots instead, and dial in the settings you want, then seal the case.

The rest of the components are necessary. As with all simple devices (transistors, tubes, etc.), their operating characteristics are determined by the other discrete components.
fatfoohy gmoon6 years ago
alright cool, thanks a ton man, i was thinking the trim pot idea myself, ill tell y'all how it goes
oh, and for a 9 pin
butthead956 years ago
what happens if you miss the switch and stomp the tube?
gmoon (author)  butthead956 years ago
The tube breaks. This is what they call a "prototype"--I had no idea if the circuit would work until I built one...
jimbowen6 years ago
Hi gmoon great instructable.. I have got all parts I need to start this project except I do not have a 12FQ8 tube but have loads of other 9 pin tubes ( MAZDA 6f23 - 30f5 etc ) Would I be able to use any 9 pin tube for the project ? Sorry if this sounds stupid I have no idea how valves tubes work Your help is much appreciated Thanks!! : )
gmoon (author)  jimbowen6 years ago
Hi, JB.

It's possible one of the other tubes might work--but not without modifying the circuit and lotsa testing. Starting from scratch, essentially (which I did.)

These low-voltage projects run the tubes at levels were they shouldn't work at all. So when I started, I had no idea if the 12FQ8 was gonna function.

(the two tubes you mention are pentodes, so the circuit would be different for certain.)
jimbowen gmoon6 years ago
Thanks for the quick reply : ) Well I do have tons of valves so I should have something I could use with your circuit ,. do different makes use different codes? I have marconi - Mazda - Brimar Vintage valves unfortunately no Wirlitzers : ( is there any way for Me to identify a suitable valve ? Thanks for the help been wanting to have a go with these valves for ages
gmoon (author)  jimbowen6 years ago
Try this vacuum tube database for identifying tubes. Just look up the code printed on the tube.

There are a few different standards for tube labeling, but unless it's British (like ECC83, ECC81, etc.), then they are probably normal USA naming. Some USA manufacturers also used their own numbering system, but they generally have the standard ID printed on the tube, also.

Lesson #1 : the first number is the filament voltage. 12AX7, 12FQ8 both have 12V heaters.

For a simple low voltage project like this where the operating voltage and the filament voltage are the same, you cannot exceed the filament voltage by more than 10%. The filament will fry otherwise. You cannot go too low with the voltage, or the filament won't get hot enough for the tube to operate. 12V tubes are the standard for the low V hacks.

The best type of tube for this kind of project is a dual triode. My "valvelitzer" technically doesn't use dual triodes (they are sort of dual triodes, but they are strange variants), so other tubes might work. But triodes are the best bet.

You might get more helpful info from the link on step 1, it's the "valvecaster," which was my inspiration...
jimbowen gmoon6 years ago
Thanks again Gmoon : ) Well I am British & in the UK, all tubes are from an ex Vintage Radio shop I will check out the database link and let You know how I get on GREAT HELP CHEERS ; )

Think Iv found one 12AT6 here is the data sheet link

gmoon (author)  jimbowen6 years ago
You've got it IDed right, I think. That's a single triode together with a dual diode, rather than a dual triode.

The triode might work, if you sting together two separate tubes. I doubt a single triode would have enough gain by itself at these low voltages.

Keep looking...
jimbowen gmoon6 years ago
Hmmmm looked at loads now the only one i can see anything like is 12bh7 If that is no good I think best to bite the bullet and buy one haha Cheers
gmoon (author)  jimbowen6 years ago
Yeah. Anyway, you've got all those valves--either sell 'em, trade 'em, or use them sometime in the future, if you fancy a normal high-voltage project...
jimbowen gmoon6 years ago
OK I will keep on looking Found 12SG7 , 12BE6 & 12SJ7 a lot of these tubes are obscure & don’t even come up on any database because they are military grade tubes + unfortunately some are so old the printing has worn away Thanks again for your help :-)
jimbowen gmoon6 years ago
Had a quick look am I looking for a Valve that has a speaker in the synaptic the ones I have checked so far have what looks like some kind of coil ( i.e HF93 ) Sorry if I sound stupid these tubes are a mystery to Me Thanks
hi. this sounds like a great project but i'm having problems. i've assembled the whole thing with a 12ax7 tube. and as far as i can tell have wired it correctly, and troubleshooted everything but i can't get it to work. help please?
gmoon (author)  HippieAdrien6 years ago
Did you build this one (ValveLiTzer), or the "valve caster" described in Step 1? The 12FQ8 and the 12AX7 don't share the same pinout--no way will the 12AX7 work with this circuit. It would work with the above mentioned "valve caster" project. Although they recommend the 12AU7 instead of the 12AX7--apparently the 12AX7 doesn't work as well at low voltages...but there would be output for sure, anyway.
i tried your version. i'm a beginner with electronics and just figured all 9-pin tubes would have the same pinout. ill give it a shot with the valvecaster since i have all these parts. thanks
hey i did it and it works. this is awesome
Ceiling cat6 years ago
Hey, do you know anything about making a guitar amp from the amp in an organ?
gmoon (author)  Ceiling cat6 years ago
I might be able to help... It's a tube amp, right?
Yes, It is a tube amp.
gmoon (author)  Ceiling cat6 years ago
OK--any specific questions?
Do you know of anywere I could find how to do it?
gmoon (author)  Ceiling cat6 years ago
IMHO, your best bet is to read up on the subject, then reverse-engineer the amp and make any needed changes. It's not really that difficult--most organ amps have similar architecture. For instance, most will have preamp, phase inverter and push-pull output stages. For some of those, it's just a matter of identifying where the tone generator is fed to the amp, and replacing that with your signal input. However, some types separate the preamp from the PI and output. I have a power amp from an old stereo like that. For those, you'd need to add a preamp stage. That's less usual with an organ, I think. You'd also need to move or override some of the controls, like the "swell" pedal and the tremolo switch, or you might be stuck with really low volume (or trem on full.)
I took a closer look at the amp and it appears that there are I would guess well over twenty connections to the amp section, which shares a chasses with the tone generator.
I have no idea where to start.
Good news I found the input to the amp, but I still have no idea what to do with the numerous connections.
muffburger6 years ago
this is the coolest thing i've ever seen ... top stuff!
gmoon (author)  muffburger6 years ago
mspark4006 years ago
great project! unfortunately i am having some difficulties. i have assembled the circuit and made an encloser but when i switch from bypass (which works) to the effect i have no sound just a little hum. i checked the tube and it is warmed and ready to go but even when i prod around to check connections I still get nothing. im sure the i followed the diagram and a got some sound earlier but it was only poping in once in awhile as i fiddled so i fixed what i thought the problem was for that and now nada. any suggestions on how i can trouble shoot or perhaps some ways to correct such a problem? thanks and cheers, mspark400
gmoon (author)  mspark4006 years ago
Could be any number of problems-- poor connections, like "cold" solder joints, a short (wired touching, solder bridge, etc.), too much heat applied to caps (shorted out), etc. Intermittent operation (and later "hum" only) usually point to the input signal either becoming unconnected or accidentally grounded somewhere along the line... Good luck.
hey i accidentally ordered a 12AT7 valve and i cant cancel it, so i might as well use it. i checked the forum for something on how to use it, but found NOTHING. i want less gain and more tubey goodness, so what do i do? i know absolutely nothing about electronics, i just solder stuff together following instructions. thanks man, Garrett
gmoon (author)  garrettanderson9836 years ago
Hey, Garrett.

Search (google) for "12AT7 Valvecaster" -- it has the same pinout as the 12AU7 that his projects uses (the Valvecaster link is on Step 1 here.)

I know that high-gain tubes like the 12AX7 don't work well for the valvecaster, but the 12AT7 is medium-gain and maybe it'll work. With any luck you'll find someone who's tried it and liked it...
i searched that and found: " Yupp...I had a 12at7 seemed real nice in the VC. sometimes, 12ax7's have so much gain they just can't seem to keep up with themselves." someone replied "You mean 12AY7?! Well, I tried the AT, and it sounded good...I believe you are the first trying out an AY... So we can say that it works good anyway!!! Yeah!!!" (that made no sense to me) i know VERY little about making electronics on my own , what i was looking for was a schematic, and nobodys made one.perhaps you would know what i could do to your design differently to fit an AT tube, like resistors i could replace and stuff. again, i dont want a lot of gain... thanks
gmoon (author)  garrettanderson9836 years ago
Completely different than my (this) project.

You needed to follow the Valvecaster link I mentioned...so here it is again.There's a schematic on the first page (and several wiring diagrams inside, if the schematic is too much.)

The pins for the 12AU7 and the 12AT7 are the same. Only the gain is different. So just build it--if it works and you like it, cool.

If you don't like it, just buy a 12AU7 and you're good-to-go. No changes needed.
oh, okay. sorry, i was a little confused, thanks! -Garrett
Hi, I'm doing the mod you suggested by replacing R3 and R4 with a 2M pot. I'm a bit confused about how to wire it in though; should I just connect the legs to 3, 4 and 8? Also, I'm using an electrolytic cap for C3, I connected the - leg to the right hand pot (and that to ground) is that right? Thanks very much for this project, it's really captured my attention! I have finished building the case now, I will post a pic of the final build at some point. Cheers, Robin
I mean right hand leg (on the wiring diagram) for P2.
gmoon (author)  planet sutcliffe6 years ago
I'm not sure how you've connected C3 (have you seen revisions on the last step? Those were put up only a week or so ago.) Replacing R3 and R4 with a single POT is an interesting idea, and not one I'd ever have thought of. Connect the outer terminals of the POT to pins 3 and 8 (the plates) and the center "wiper" terminal to pin 4 (the positive voltage.) Those two resistors are the "load," and (in general) when you increase the load you get more voltage gain. There's always a price to pay--more voltage gain means less current output, so the output impedance could rise high enough to degrade the signal. You just have to play with the values to find the right sound. A POT here would let you move the gain dynamically over both stages of the booster, which could give you some interesting sounds. Turn the POT one way and the gain is concentrated in the first stage; turn the other way and it's in the second stage. I would add a resistor (47K to 100K) between each plate and the POT--that will prevent a "no load" situation, which would be no gain at all in that stage (blocking the sound entirely.) When you turn the POT to it's extremes (each end of the rotation) the resistance will be effectively zero, which would be no load.
Hi, Thanks very much for your advice. I will try that (need some more resistors first though!) The thing is about C3 I have finished my case design so I can't really connect another pot meter (also I have 3 nice pot covers I took off an amp I found in the street - these are also part of the design) So I have connected C3 in accordance with the original wiring diagram/schematic, with the negative leg of the cap (electrolytic 47uf) going to the right hand leg (on the original wiring diagram) of P2, which also connects to ground. (this seemed logical to follow the current) Is that right? I had thought about maybe adding a 50k trimmer pot for the revisions made to C3, as this is the only way I can get it in the case. Would that be a workable idea? I love lots of control over the sound, the more I can add the happier I am! Thanks again, Robin
gmoon (author)  planet sutcliffe6 years ago
Sure, you're welcome... C3: Yes, connecting the negative (-) side of a polarized cap to the P2 POT tab that also connects directly to the GND is the correct way to do it.
gtkid20026 years ago
Ahh! You update the schematic the day -after- I buy all the parts, haha. Oh well. So what do you mean when you say the new schematic has "More Power"? Perhaps a sound clip is in order of the new and improved sound? Heh, Soon as I saw this, I knew I had to make one. Looks and sounds awesome man~
gmoon (author)  gtkid20026 years ago
Thanks--I shouldn't apologize for improving it, right? ;-) I'll have to add sound clips at some point, but it may be a week or two.

There's definitely more gain (and distortion) now. When I first built it, I was looking for a "tube sound," but without too much distortion. The bypass-cap gain control can be "dialed down" with this mod, so it'll still get the old sound. It's just more versatile.

If adding a third POT is too much, you can always add another cap in series with the original, and switch it in-and-out with a small switch...

Lets face it--most people want more from a stompbox (especially if they're using a flat-sounding SS amp.)
gtkid2002 gmoon6 years ago
Yeah, more is generally better in a stompbox. And no, you should not be apologizing for improvements. I've ordered the parts I need for the improvement, but I get to build it tonight. How much does this flavor the sound when it's not being overdriven? It's tempting to use the schematic for a home audio setup, but use a regulated PC power supply. Constant 12 volts of pure sine : ) But yeah, again, kudos on the design. You have no idea how excited I am to finally afford something that's tube. Thanks for using cheaply priced tubes by the way! Entire project is going to cost me a few cents under 40 bucks, which is a little high compared to the silicon fuzzes I normally make, but eh, this is TUBE! Tube is awesome.
gmoon (author)  gtkid20026 years ago
Tubes are awesome.

Re: the stereo question--one of the positive characteristics of tubes is even-order distortion (mostly second order), which sounds a lot like the "fundamental" note and is generally considered pleasing to the ear. Transistors don't do even-order distortion (although mosfets can.)

But (almost all) guitar amps push beyond that, adding odd-order distortion for "bite," because even tube amps would be a little boring without it.

I suspect that like most guitar tube preamps, this one is more odd than even distortion. I think this for two reasons:

1) the operating voltage is so far out of spec (low), I wouldn't expect it to perform normally.

2) Tubes and transistors are "current out" devices. To make them run as "voltage amplifiers," we add a load. Thanks to "ohms law" (E=I*R), if we want more "voltage output" from a specific amount of current, we need to increase the load resistance (it counter-intuitive, but true.) The current output suffers (the output inpedance rises), but that's the game...

In a normal triode gain stage, the amount of second-order distortion decreases as the load resistance increases. For a typical 12AX7 stage, a 68K load resistor might be 7-8% second-order, but a 220K load would be 2-3%.

Since the only way to squeeze out gain from a low-voltage setup is to raise the load resistance even higher, this project has 470K (R3) and 1M (R4) loads. It's likely mostly odd-order distortion. However, since the tube is running on voltage so far out-of-spec, the tube characteristic charts are worthless, it's just a guess.

Stereo amps usually have very low odd-order distortion. Maybe this project, if adjusted correctly, would "warm-up" a SS power amp, I don't know. I think it would get pretty nasty fast, though.

(I still wouldn't call this one a "fuzz"...)
gtkid2002 gmoon6 years ago
Well, what about if it was the frontend for a 386 amp, like you suggested?

That could make a nice small "at home" headphone amp at least. I know there's no way this could power something huge, but headphones, I think it could drive those well at least.

I don't have much experience with tubes, but correct me if I'm wrong on this:
By increasing R3 and R4's resistances, it's possible to lower the distortion that the tube produces, if only by a minor amount? I know that would also lower the output, but if it was backed by a small SS amp, it could at least probably power headphones.

But yeah. This thing roars. Finally finished it at about 4am last night, and Nngh. I haven't heard anything quite like that in all the pedal's I have made.

I wasn't trying to call it a fuzz, so my apologies. I just normally make fuzzes, and on the parts list, compared to a fuzz I normally make, this is pretty spendy. A five dollar tube Vs a six cent transistor. Litttle bit of cost difference on that alone.
gmoon (author)  gtkid20026 years ago
But yeah. This thing roars. Finally finished it at about 4am last night, and Nngh. I haven't heard anything quite like that in all the pedal's I have made.

I wasn't trying to call it a fuzz, so my apologies. I just normally make fuzzes, and on the parts list, compared to a fuzz I normally make, this is pretty spendy. A five dollar tube Vs a six cent transistor. Litttle bit of cost difference on that alone.

So--how's it sound? do you like it?

Don't apologize--I'm only pointing out that a "fuzz" is a pretty extreme distortion style, which I'm not claiming this is...

I'm sure you could run this through a 386, for headphones or mini-amp. I'm not certain it's gain is enough by itself for headphones, but I haven't tried it.

I don't have much experience with tubes, but correct me if I'm wrong on this:
By increasing R3 and R4's resistances, it's possible to lower the distortion that the tube produces, if only by a minor amount?

Raising the load resistance lessens the "second order" distortion. Once you pass that point, distortion is mostly a "clipping" issue. If you push the gain so high that the waveform peaks clip on "the rails" (the positive and negative power supply limits), you're gonna get odd-order distortion (third-order, fifth-order, etc.)

That's what gives "bite" to an amp, but too much "odd-order" and no warm second-order, and it becomes the harsh solid-state amp sound. Hopefully, this retains both types.

It's not just the gain that effects the clipping--it's the bias. A tube has to have a "negatively biased grid." Like charges repel each other-- the cathode is the source of electron flow (negative charges) so the grid is the "valve", and keeping it more negative than the cathode, it prevents the current from flowing to the plate. Make it too negative and no current will flow even if you apply a signal variation to the grid.

Bias the grid just right, and varying the input signal will let a proportional amount of current flow from the cathode to the plate.

A "cathode biased" stage achieves a negative bias on the grid by raising the cathode voltage above the ground with a resistor. The P2 POT is that resistor. By adjusting the setting of P2, you can change the "reference voltage" for the cathode. This POT lets you throw the bias "out of whack," intentionally clipping the signal.

So--to get less distortion, you have to feed each stage with just enough, but not too much signal, and bias it so it's not referenced too high or too low that the peaks are clipped.

There's an inherent limitation here--the low voltage of the amp. Solid state amps are often low voltage, too. That's OK, so long as the power stages can push enough current at the lower voltages to move the speaker coils...
gtkid2002 gmoon6 years ago
How does it sound?
AWESOME. It's got a nice amount of gain, and when I use it after Runoffgroove's Fetzer valve ( See here ), it just completely overdrives. That would make a nice pre-whatever to get it straight to overdrive, but it renders the bias knob useless for the most part.

Mind you, I play bass. I've got a Jeff Berlin Signature Series, the old 3 knob model, and I've tonemodded it. So everything sounds different for me.

I'll hopefully be able to try it on a Fender Mexi-Strat that was made in the mid to late 90's, on a Fender SS amp. I don't know/remeber the model number, but I'll try to get a recording. I didn't realize this tube would take as much power as it does, so right now it uses my camera's 4 AA's, and four more.

I think if I were tweaking this schematic, I would probably add a tone section. Or figure out how to add a small clipping section after the tube that has a selection switch, so I could switch it to blues or something. Blues and tubes just seem to go hand in hand to me.

But yeah, I love the sound this thing makes. I'll see if I can't get a decent recording of it sooner or later.
gmoon (author)  gtkid20026 years ago
Ah, cool, glad you like it.

A simple low-pass tone control would be easy to add. The inspiration for this project, the Valvecaster, has one (similar to what's in a guitar or bass.)

You want to "voice" this for bass, instead of guitar?

Increase C1 and C2 to 0.02uF, instead of 0.01uF. This will increase the bass response. If you're always running with the FX volume control turned down, you might even increase C2 to 0.033uF.

Caps in parallel are additive, so you could try it by adding another 0.01uF cap together with the existing cap. Then it's easy to remove if you don't like it...
And I forgot to mention this, but I like your choice of containers. I know they were probably just lying around, but it looks good. It looks classic almost, I'd make one and just hide it away somewhere, just because of how awesome it looks.
jackillac926 years ago
So I built this and it effects the way it should but when I used it I noticed that the volume is SIGNIFICANTLY lower than in bypass mode.Why is this the only difference in parts is that I used a 20K potentianometer rather than a 25-50K potentianometer. What else could be doing this because whenever I use it it effects the signal well giving it that tube sound but the only problem is that its at about 25% volume and when I push bypass it goes back to the normal full volume.
gmoon (author)  jackillac926 years ago
Could be a few things, including wiring errors. Check your layout carefully. Are the components (other than the tube) brand new, or recycled? And what type of amp are you running the signal into? I've only tested with guitar amps. Also, look at the newly-added last page, which has a "gain mod." Upping the value of C3 increased the gain significantly. It was one of the modifications discussed on Step 7... Before that mod the project always boosted above unity gain, although it varied from amp-to-amp as to how much boost (probably related to the input impedance of each amp.)
I was thinking that it may be a misplaced resistor somewhere which is resisting the signal making it very weak. I thought that it seemed logical enough what do you think?
gmoon (author)  jackillac926 years ago
It's hard to debug a circuit over the internet--there are too many potential problems. Anything from an incorrect connection, to an unwanted solder bridge (short), to incorrect components (substituting a 47K resistor when 470K is called for, for instance), to a cap that's failing 'cause too much heat was applied during soldering... The reasons for circuit failure are many.

But sure, you should very carefully trace your connections.

If you can post a picture of the wiring, that would help.

Are you sure the power source is between 9V and 13V? It will quickly get quieter if you're using a worn-out 9V battery. It will exhaust a new 9V battery in an hour or two...
I will try a new 9 volt battery then. But I can still see part of the tube warm up at three different points but its not quite "Glowing" per se, at the end of two of the wires inside the tube it looks almost like an ember from a hot fireplace, the tube is definitely getting power but I just dont know if it is enough power, im using a 9 volt battery BTW. Thanks for helping me I apreciate it!
So I changed the old 9 volt out and I can hear a difference and the volume has gone from about 25% of the normal volume to about a full 50% of the normal volume I also rechecked my resistors and everything seems to be in check around the tube socket. Also I was wondering I wasnt sure if the pot was "linear" I do know that the pot I am using is the 500k with the .01 cap and th eother pot I am using is a 10k pot with a 1 NF capacitor between the two lugs as described in your diagram.
gmoon (author)  jackillac926 years ago
An Audio taper pot has a much more natural gradient--but set at "full", a linear taper pot should still give you the same output. It will just drop off really quickly as you turn it down.

It would be helpful if you give me the component label from the diagrams--i.e., C3, R2, P1, etc., so I know which part you're referring to...

There should be two 0.01uF "coupling capacitors"--they're placed between each stage, and block any DC offset voltage (which would mess with the bias of the next stage.) If they are any smaller than 0.01uF, there will be volume loss.

1 NF for C3 is way off. The bypass cap is 0.1uF; 1nF equals only 0.001uF. This may have a lot to do with the lack of gain you're experiencing.

And at this point, I'm recommending a much larger value now for C3 anyway for max gain--over 10uF (I've been using 100uF with the new, third pot.) Any value such as 22uF, 33uF, 47uF will boost the gain. You don't need to add the third pot (see the new schematic on the last page), but you should up the cap value.

Sorry to have changed the circuit--but I'm always trying to improve my stuff...

10K for the bias pot is also pretty small--the signal tends to get more square-wave shaped (fuzzier) in the 25K+ range...
Hi, I have this switch (link attached) which I'm planning to use for the bypass. It's am SPST, but I am not sure whether it will work for the application. I'd like the LED (in the switch) to be lit when the bypass is off (ie effect on). Am I able to use it for this or should I keep looking for a different switch? Thanks very much for your help, and such a wicked instructable, I'm really enjoying making the case at the moment, I will post a pic of my finished build when it's ready.
That's the link to my switch there, It didn't post in the original! Thanks again.
gmoon (author)  planet sutcliffe6 years ago
Hi there. I see the switch, but it's not good for bypass. That one just connects / disconnects a single line (it's completely open when off.) You need at least an ON/ON switch, i.e., when it breaks one connection it makes a second different connection.

That's the minimum required to bypass, which is the type I used-- but even that's not "true bypass."

Here's an example of a switch can do "true bypass," and has enough spare contacts left to switch a separate LED power indicator, too.
Hi, yes I have been following the revisions to the design by yourself and by Jeff-O; I'm going to include 1000uf caps to filter the power supply, some LEDs for underneath the case (and maybe below the valve itself). I also saw your advice to use around 47uf for C3, I'm on it. I'm replacing R3 and R4 with a 2 Meg pot also, as you suggested. I'm planning on using a regulated wall wart with selectable 9v or 12vdc, so you can get the "more tubey" effect at 9v, and get more compression at 12. Thanks again for the advice on the bypass switch,
gmoon (author)  gmoon6 years ago
Also, see my note below about increasing C3 to a higher capacitance value...something like 33uF or 47uF... I need to update the schematic, sorry about that...
22bsti6 years ago
Would a 12AX7 tube work for this?
gmoon (author)  22bsti6 years ago
Sorry, the 12AX7 is completely different. You might look at the "Valvecaster" (link on Step 1)--the 12AX7 pinout would work, but I believe the general consensus is that the lower mu tubes like the 12AU7 work much better in low-voltage projects.
22bsti gmoon6 years ago
Thankyou very much for your help. I'm young and I don't overly understand how tubes work but I think I've got the idea after reading through the link you gave me.
dadadata6 years ago
Craig Anderton did some tube designs for PAiA Electronics using starved tube circuits. Maybe 1985-1990. Believe they're still sold.
gmoon (author)  dadadata6 years ago
Thanks for the info. Craig's one of my heros--I bought "Electronic projects for Musicians" way back in college (1978) and it was my introduction to guitar-related electronics. It wasn't my first foray in electronics, but it's the stuff that kept me interested...
dadadata gmoon6 years ago
I built a bunch of his little things back when Godbout Electronics sold the circuit boards.
Ceiling cat6 years ago
Hey. Last week was moving out day at the college I live near, and I found a still working Lowrey organ dumped upside-down next to a dumpster(such a shame). I took it home, and it has 5 12AX7, 39 6X8, and 1 12AU7. I was wondering if it would be possible to substitute one of these tubes for the 12FQ8, perhaps with some modification. Great project by the way. Beautiful tube sound, and very nice choice of case. Looks very vintage and minimalistic.
gmoon (author)  Ceiling cat6 years ago

I'd say you did well: 12AX7's don't work well at low voltages, but are THE preamp tube for guitar amps. They are also found in HV preamps, like the Real McTube. If you know anyone with a tube amp, they'd love to get a hold of some vintage 12AX7s...

The 6X8 must have been used in a similar fashion as the 12FQ8, but it's different enough that you'd have to start from scratch to get it working.

But you did luck out: the 12AU7 is the basis of the Valvecaster, which was the inspiration for the ValveLiTzer. There's a link on Step 1 that will get you to the project. Good luck!
Thanks. I looked at the Valvecaster and it is my understanding that it requires 2 12AU7, but I only have 1. This would be a problem.
Oh. I see. He just split it up so that he could fit it on the schematic. Sweet! I'll have to make this.
gmoon (author)  Ceiling cat6 years ago
Yes, you figured it out. The 12AU7 is a dual triode--two separate valves in a single tube.

It's normal to separate circuit building-blocks on a schematic (opamps, for instance) that physically may be in a single "package." That's the difference between a schematic and a wiring diagram. Wiring diagrams represent the physical, schematics are conceptual...

Conceptually, a 12AU7 is two separate valves...even if they're packaged together.
jackillac926 years ago
Exactly what type of switch is it? I cant really find any "ON/ON" variety switches.
gmoon (author)  jackillac926 years ago
Search for "guitar footswitch DPDT", here's an example.

The DPDT type is a little more complicated than what I used (single pole), but you could configure it as a "true bypass". Or it could be wired same as mine, you'd have a choice.
jackillac926 years ago
What are the resistor values the picture is VERY hard to read. I can jsut barely make out the capacitors to. Please do tell?!
gmoon (author)  jackillac926 years ago
Load the separate PDF just below the schematic. That should help ;-). It's not an "official instructables PDF," it's one I made myself...

I'm now recommending that people increase the value of C3 (anywhere from 2.2uf to 100uF, depending what sounds good) to get more gain from the circuit. A larger cathode-bypass cap == more gain and bass response.

In a few days I should have a new PDF with a couple more changes...
DeMinstrel6 years ago
Nice project!...very cool! Can this be modified for a CLEAN boost? Your comments please. Thanks.
gmoon (author)  DeMinstrel6 years ago
I answered you once before; I don't know why it never showed up...

As is, it's not heavily distorted. But I suspect running the tube at higher voltage would be better for a really clean signal. Then the component values (plate resistors, etc.) could be replaced with more normal ones, and the boost should have more headroom.
pyrohaz6 years ago
Would you ever sell these... Its a lovely sound!
gmoon (author)  pyrohaz6 years ago
Thanks! Right now I don't have any plans to sell any (I would like to keep updating and improving the design, though.)
vampiresk86 years ago
-Very cool project, I want try to build it but I havent a 12FQ8 tube.I Italy is not simple found its, but I have 12AU7 tube and I want to know if is possible use this tube without any mod of the schematic tha you use. Thanks a lot man, for all!
gmoon (author)  vampiresk86 years ago
You shouldn't use my schematic with a 12AU7 tube, but you're in luck--just follow the link above (in Step 1) to the Valvecaster. It's a 12AU7 project, and just as simple.
Traverse6 years ago
I found a clear plastic box that I hope to use for mine... Since the tube lights up and I want to keep it from getting bumped / broken I thought about installing it inside the box... Would I need to vent the tube?
gmoon (author)  Traverse6 years ago
In a plastic enclosure, yeah, some air vents would be good. Personally, I think metal does a better job of shielding (less noise.) It why traditional tube designs used metal chassis.
Traverse6 years ago
Great project - thanks! You mention combining this with a 386 amp on the front end... I can see the obvious way of connecting the two, just setting up the amp with a 1/4" plug and run a cable between the two. I'm actually looking for a cheap, easy to build first tube amp project and the ValveLitzer plus a 386 amp sounds like it might be one of the easier ones... Any other thoughts on how to hard wire the two together? I've been looking at the Little Gems amp from Runoffgroove as the other half. Any other thoughts?
gmoon (author)  Traverse6 years ago
You might look into existing projects that combine the "valvecaster" (12au7, see the link in the story) and the "ruby" amp. They've already done most of the work for you. But this project plus the ruby should work. I doubt it would be difficult to wire the two together. Obviously this would act as a preamp for the ruby--maybe just play with the coupling caps between each device.
Traverse6 years ago
I should add that I did see the tube amp build on the instructables site... Little bigger than I was hoping for but will probably try in the future as well.
acaz936 years ago
lucky you! you have 25+ tubes whereas i have zero ! and for mere curiosity , how did you got so many tubes ?
gmoon (author)  acaz936 years ago
See the pic on Step 1; it's the tone generator in a freebee WurliTzer organ. If my memory serves, there were 28 of the 12FQ8 tubes in there...

I have a lot more tubes than that...different kinds, of course.
acaz93 gmoon6 years ago
Do You know if , for example , I can use this kind of tube as a stand alone Amp (ie. for powering some speakers , with an iPod as music Source) ?
gmoon (author)  acaz936 years ago
It's theoretically possible, but not at these low voltages.

I've seen some small signal triodes used as output tubes. The Firefly Amp is one such project. It uses both sides of a 12AU7 for the output tubes. But it's total wattage is only 1/2 watt, and it's running on 265 volts.

A power output pentode tube (6V6, etc.) can control much more current, and is the normal solution (don't ask me about low-voltage operation, though. I've never tried it on a power tube....)
acaz93 gmoon6 years ago
265 volts , golly gee !
gmoon (author)  acaz936 years ago
That's a fairly normal voltage for tubes (although the "firefly" output tubes probably don't see that much voltage individually, since it's are setup in an oddball split fashion, yet not a typical push-pull configuration.) Still, 250V+ isn't unusual. The low-voltage projects like this one shouldn't even work... The tube in my project (12FQ8) has a max plate voltage of 250V.
ogorir gmoon6 years ago
a firefly is self-split push pull. both tubes still see the full B+ voltage, it's just horribly inefficient. quite a lof of mods have been done to that circuit since John Calhoun started running off PCBs for it, the most popular of which is changing the output tube to a ECC99 for about 2.5w out.
acaz93 gmoon6 years ago
With the couple of tubes i've worked on the maximum voltage was about 48 volts , compared to 265 thats a BIG difference ,ain't it?
gmoon (author)  acaz936 years ago
Yep. Those were tubes for battery operation, maybe. Even the battery tubes I've seen had max voltage near 90V...
DIY Dave gmoon6 years ago
I have about 8 tubes out of a junk organ.
gmoon (author)  DIY Dave6 years ago
Anything good? What types / models are they?
never mind i found a store
if not, could i buy one of your 12FQ8s. Please
could you change the tube to a 12Ax7? i have no places to find a 12FQ8.
pyroarchist6 years ago
hey man whats up! this is stupidplants from YouTube. there any way to mod this into a pedal with extreme high distortion,punchy bass, and screaming highs? (such as Mesa-Boogie or Krank style distortion)
hey, I have a bunch of 12ax7 tubes can I use one inplace of the kind your using? and if so, what kind of changes would I have to make.
gmoon (author)  jjelectro6 years ago
I think you're replying to the project (rather than pyroarchist). You might check out the "Valvecaster" link on Step 1. It uses a standard 12au7. However, if I recall correctly, 12ax7's didn't work nearly as well at low voltagesas the 12au7's....
gmoon (author)  pyroarchist6 years ago
Hey, not much, what up with you? The low-voltage nature of this project prevents it from being "bees-in-a-can" type of distortion--a two-tube version (mentioned on the last page) might be closer to what you're lookin' for...
I think I just found my next project. Can't wait to start tinkering. Thanks.
Koil_16 years ago
Any chance of using one of the tone banks as a modulator for a guitar? Just a thought...
gmoon (author)  Koil_16 years ago
Hey, Koil.

I've been thinking the same thing (as have others, if you search the web.) The 12FQ8 tubes were used in a frequency divider circuit, and some sort of octave effect is theoretically possible. But the dividers in the organ are "tuned" circuits (resonant frequencies set with inductors), which wouldn't be ideal. That's not to say they have to be tuned, though.

I have looked at the original WurliTzer patent on the circuit, and I don't think it's possible at low voltage--at least not possible with tubes only. There's not enough gain at these voltages.

If the signal level could be raised with transistors, that might be a start... But it would be challenge.
Koil_1 gmoon6 years ago
I just started on an old Hammond oregon's tone banks. It uses the standard 12ax7 tubes but it's a start. I'm winding my own inductors to use in conjunction with a 7 position rotary switches that I scavenged from an old printer selectors. I'm actually considering wiring all 7 banks into what will be more or less, a mixer console to control frequency, tone, and wave form. Bassicly an old school synthesizer that uses a guitar as a carrier signal. In theory it would also be possible to use it as a vocoder which is a plus. It's obviously going to take a little tinkering but I'll figure it out. This is by far the most extensive tube project I've ever undertaken so it'll be interesting at very least. Thanks for the great instructable and the inspiration. You have honestly made my life a better place for me. I just wish there were more people in the world like you friend.
gmoon (author)  Koil_16 years ago
Cool project. With the inductors and all, it will certainly do something, even if it's the just an awesome tone shaper. And 12ax7's are always usable for something (most common preamp tube in all amps.) That's a bonus. I've collected about thirty five 12ax7's from various organs ;-), more than enough to play with. Thanks for the kudos, man. Good luck, rock on.
how do you drop the r 3 to 220k
gmoon (author)  kiteboarder926 years ago
R3 is set at 470K on the schematic. Just substitute a 220K resistor for the 470K value.
jeff-o6 years ago
Just a small typo: In your parts list, change the tube number to 12FQ8. I was going nuts trying to find a 12BQ8 online!
gmoon (author)  jeff-o6 years ago
Ooops...sorry about that. Fixed. Thanks for the "heads-up." RE: the pots-- one is audio, one is linear. The parts list on that page was old (I started writing this in Nov., but the design has changed.) I fixed that, also. The volume is audio, the bias control ("bite" of the effect) is linear... A more complete parts list is on the "Build" drawing on Step 4.