DIY tube overdrive pedal

[BigBadWolf1171]

that looks way to easy haha. I don't doubt that it works, I just would have guessed something more complicated. I have no idea what i'm talking about though so don't mind me.

Apparently the guy builds these often, But im like you,i havent a clue with these things. Maybe one of the fellows here with better knowledge will provide some insite.Id love to see one of these things with 2 or 3 tubes in them.

[tunghaichuan***]

Apparently the guy builds these often, But im like you,i havent a clue with these things. Maybe one of the fellows here with better knowledge will provide some insite.Id love to see one of these things with 2 or 3 tubes in them.

That circuit is similar in concept to the BK Butler/Tubeworks Tube Driver. Since there is only a 9v supply, the tubes operate in "starved plate" mode. Preamp tubes normally operate on 100v-300v. It's similar to using a Variac on a tube amp. When there is only 9v on the anode the tube operates way outside its linear amplification range and is easy to push into distortion.

There are several overdrives similar to this one, like the Dean Markley Overlord.

If you want to roll your own BK Butler Tube Driver, there are a few threads on freestompboxes.org. PCBs, graphics, the whole enchilada.

[duhvoodooman***]

If I ever get ahead of my other projects, I gotta try one of these....

[BigBadWolf1171]

If I ever get ahead of my other projects, I gotta try one of these....

what made it interesting to me (other then it doesnt look to hard to build), is i use a solid state xxl peavey amp, and it allows you to put something in the preamp (pedals etc).while the amp is a real good SS amp, it has no real "tube sound", so one day i took my ibanez tube king pedal (has a 12ax7 tube) and plugged it in the preamp and maaaannnn was i suprised at how it sounded, like a totally different amp. So anyway i was wondering if there was a way to make this pedal with 2 or 3 or more tubes in it, as i could run it in the preamp, but ive never attempted making a pedal before.any idea?

[jim p]

The tube in the circuit looks to be for decorative purposes only and all the battery does is light the LED. I drew the circuit out and the only pins on the tube doing anything are the heater pins 4 and 5 passing the signal. So at best the heater element is being used as an inductor in the signal path. There is no current supplied to the heater so no space charge of electrons in the tube so how could the tube work? If you want to make a tube overdrive with low voltages they used to make tubes for car radios that work with a 12 volt supply. I have built an overdrive with one before and am now building a vibrato/tremolo and overdrive box with one now a 6GM8.
I can post a schematic of the posted circuit to give you an idea of what it is, some people would call it a signal canceling noise enhancing circuit.

[tunghaichuan***]

Edit: the Westbury tube OD runs at high voltages and doesn't operate in starved plate mode.

Another project to check out is the Real McTube OD. I built the first version that came out in Feb. 1999 issue of Electronics Now. The newer version can be found here: http://www.dogstar.dantimax.dk/tubestuf/mctube.htm

[jim p]

I did up this quick schematic for a tube overdrive using the 6GM8 tube. Do to the low grid resistor required with this tube there is a jfet buffer a J211 as the input which is also used as a tone control. The schematic program does not have symbols for pots so R3-R4 represents a 10 k pot. Also R19-R20 and R21-22 is a dual 100k pot used as the gain control. While R23-24 is a 1 meg audio pot for the output level control. The two triodes have current source loads in the plate circuits using 2N5457 jfets with 750 ohms in series with there source. What is not shown is the power supply section which is a rectified 12 volt AC supply that is also used for the heater with an approx 18 ohms 5 watt resistor in series. The final output buffer FET could be optional if you are connecting to a tube amplifier, required with a solid state amplifier. C10 and C11 are brightness (treble boost) that has been added and one or the other could be removed or values could be increased or decreased to your preference. You may want to add a resistor in series with the tone pot (R3-R4) to limit the maximum gain with the tone at maximum.

Took a break to see about the cost for the tube and not sure but looks like they are going up in price. The tube you can use is a 6GM8/ECC86/2N27P getting to be 20 bucks each.

Here is the basic schematic
http://i1020.photobucket.com/albums/...8overdrive.jpg


Here is a page on space charge tubes
http://www.junkbox.com/electronics/l...agetubes.shtml

This whole thing made me look around and what I think would be away to go would be to modify one of these. http://pro-audio.musiciansfriend.com...amp?sku=180581
I need to check out the schematic but for 30 bucks you have the box the tube the power supply hard too beat, just need to see what it would need to be used for a guitar.

[DeanEVO_Dude]

The tube in the circuit looks to be for decorative purposes only and all the battery does is light the LED. I drew the circuit out and the only pins on the tube doing anything are the heater pins 4 and 5 passing the signal. So at best the heater element is being used as an inductor in the signal path. There is no current supplied to the heater so no space charge of electrons in the tube so how could the tube work? If you want to make a tube overdrive with low voltages they used to make tubes for car radios that work with a 12 volt supply. I have built an overdrive with one before and am now building a vibrato/tremolo and overdrive box with one now a 6GM8.
I can post a schematic of the posted circuit to give you an idea of what it is, some people would call it a signal canceling noise enhancing circuit.

Hi jim,
Do you know if those are those the same tube used in the ZVex Nano?

By the way, thanks for all the tech-talk info in the "Crate V5 mods" thread, great info. I am picking mine up this weekend ($50 used at GC).

[jim p]

The 6GM8 is the same size as a 12AX7. In the Nano they use miniature tubes and a have a switch mode power supply to get the plate voltage of approx 250 volts. The smaller a tube the shorter its lifetime also the tubes in the Nano are soldered in so? If you want a low wattage amp I would build a Firefly for a lot less money. Ted Weber has the transformers cheep and the board is 20 bucks.


You could also consider adding a variable voltage regulator to the Crate V5 if you are modifying it for a low volume overdriven sound in that mode the power tube should last a long time.