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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.
.
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.
.
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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...)
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...)
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I'd like to label the pots, but not sure what the correct terms would be. Gain, bias, volume, tone..etc?
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...
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...
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...
if not what is the differance between the 2 circuits that make the the tube not interchangeable?
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:
12FQ8
--Dual plates for each valve (four total).
--A single, shared cathode for both valves (one total).
12AU7
--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 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
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. ;-)
The link itself:
http://frank.pocnet.net/sheets/127/1/12AU7.pdf
Here's a scrn capture of the pinout. And the other tubes in that family (12ax7, 12at7, etc) share the same pinout.
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?
12au7
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.
12FQ8
(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.
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...
how does this look to you?
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.)
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.
-and-
What kind of switch would you suggest for your V0.4 Valvelitzer?
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...
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!
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...
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
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...
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...
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!
http://www.youtube.com/watch?v=NQzcp6w5-to
http://www.youtube.com/watch?v=JNj_qWWSl3U
Thanks!
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...
Thanks for a very cool instructable!
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.
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. :)
Thanks!!
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.
Thanks!
-- 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...