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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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
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'll go there but I'm far from tube savvy I just know how to solder a circuit together
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.)
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?
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...
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).
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
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...
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?