DIY tube overdrive pedal

[jim p]

I found this while I was looking around on starved plate operation http://www.instructables.com/id/The-...-Tube-Booster/
I can’t be sure of how well it works but I would look for control grid current which will be a negative voltage at the control grid because that current will be flowing through your guitar pickups if you plug straight in.

[jim p]

I still need to finish off the box I started with a 6GM8 that is an overdrive and tremolo but just not up for drilling holes today, so. I grabbed up a wall wart 9 VAC transformer from an old dial up modem and built up a voltage multiplier for 55 volts DC to check out one of the 12FQ8 tubes I got in the other day. I found a patent at Google by the Wurlitzer Company for tone generators that used these tubes and the tube has Wurlitzer on it. With the tone generator they could use one plate for the oscillator and take the signal at the other plate so it would not load the oscillator down. With a plate load of 500k, a 100k grid resistor and the cathode at ground I am getting a gain of approx 50 from the tube with both plates tied together. The grid current is 800na with one plate and drops to 600na with the two plates connected. The plate current is approx 60ua. The heater voltage is 10.2 volts AC. The maximum input signal before distortion is 500mv peak to peak, signal level at saturation is 1.2 volts peak to peak. The tube has a gradual slope going into cutoff, wish I had a 12AX7 waveform to compare it too I am sure the 12AX7 would look different more squared off. I need to connect up a jfet buffer on the input due to the 100k grid resistor and a emitter follower at the plate to not load it down to maintain the gain then see what the tube sounds like.

[jim p]

Has anyone out there tried the ART mod? I am going to post a sound clip of how it sounds soon I hope. I was going through buying the required parts caps, diodes and a transformer from Mouser for the power supply coming to approx 15 bucks without shipping. Still need a tube and tube socket figure 10 bucks, then switches pots a box, hard to beat the 30 bucks for the ART. Anyway be interested to hear if anyone has tried this out aside from me, thanks.

[jim p]

Well do to the fact that people are looking at this post I have a question. I have made some small PCBs for adding the Belton Dig-reverb to a tube amplifier and also a small push pull amplifier http://www.thefret.net/showthread.php?t=15442 So even though I think the cheapest way to go is to modify the ART tube MP I could make a PCB for a tube overdrive.
Would try to make the board 2.5 inches x 3.8 inches same as the other boards. Would have gain control, tone control, tube bias switch and output level control. There would be a boost switching supply to operate a 12AX7, 12AY7 or 12AZ7 tube with an approx 220 volt plate supply. Power would be a 12 volt probably AC or DC wall supply. A guess at the total parts cost would be approx 100 bucks.
Anyway I have the small amp to finish off first let me know if there is any interest.
For what it is worth the small tube amp is approx the same cost and can also be used for a tube overdrive.

[jim p]

Two sound clips of the Art Tube MP modified to be a tube overdrive. There are two clips one at low gain, the other at the high gain setting. Played through a modified Crate V5 with a Weber Signature AlNiCo 8 inch speaker.

[jim p]

Right now Music123 has free shipping at 29 bucks so you can get the ART Tube MP for 30 bucks.