Been on a fuzz building kick lately. 3 rangemasters, fuzzface, Maestro fz-1, etc. Bought some more pcb's for fuzzfaces, more rangemasters, astrotone (sam ash fuzz), couple simple boosters (npn, pnp, fet, LBP, Electra). Came to the conclusion that it's easier to find tubes from the 20's than to find certain transistors from the 60's -70's. Will not try to think about using IC's such as lm308 and those bucket brigade things. Next hamfest i will be more equipped with lists of stuff to look for. Anyway, in my tube stash i have about 150 pieces of 6211, it is basically a 12au7 (low gain) that was used in computers way back in the 50's-60's. I tried to use these back 30 years ago in guitar amps and all they did was howl, terribly microphonic. The point is, the circuit i tried to use was meant for 12ax7, as are 99% of tube guitar amps out there. The whole family of 12A*7 have the same pinout but different gain, different everything. Fast forward so fast you are seeing UFO'S. Light bulb goes on. Long lost project comes to fruition. Got a deal on some (36 pcs) small transformers, 80% off list price, (sucker for large quantities of electronic stuff i will never fully use) Triad, dual 12 volt secondaries. Tube pedal time. For enclosures i think i may be able to use 1590c but this thread is about the breadboard guinea pig that is alive. Building the circuit around the parts you have. The Valvecaster uses either 9volt or 12volt to power the entire tube. Thanks to Matsumin for the initial build and webpage dedicated to it. It's known as a starved plate design when running the tube voltage well below what would normally be used. Transformers are giving me about 20vdc for the plate and the other winding, once dropped a bit, gives me 12.6vac for the tube filament in series mode. I'm not going to get into how modern "tube" pedals are claiming "starved plate" mode when they are still using a 12ax7, they just don't work with low voltage and sound like crap. They do work but not in true starved plate mode. 12AU7 and other tubes work much much better on low voltage. They are much cheaper in NOS form too. That's all i know, 2 zinc cents worth. BK Butler Chandler pedals used a 12ax7 so i am gonna have to study the schematics from them and see what he did there. Here is the flea market enclosure i built it in for now. It works, it jams, not quite a fuzz or distorion. No rangemaster Sabbath tones, but more general rock, Skynyrd, Billy Thorpe, Crazy Horse dirt. Most parts except the power supply are soldered right on the tube socket itself. Once i figure out how to put a small transformer and a tube socket on a 1590c, i will be much happier. Don't ask about the meter, it's not hooked up, i just wanted the slant project cabinet. Here is the distortion meter showing 37.5% dirt and the oscilloscope showing what that dirt looks like, it removes the original signal and shows you the distortion component. Weird waveform but as i said, not as much heavy fuzz with sub-octave low notes. Testing was all done at 1khz and 70mv. Next page will just be 3 pictures, the original schematic, my few changes i made to the schematic, and a final tube chart showing tubes i tried, about 30 different ones, distortion measured and gain measured. I didn't like the gain pot on the tube cathode. Every time you adjust the pot, you hear scratchy noises. That's because there is voltage there on the cathode (duh) and pots don't like voltage on them. Why it was made like this i don't know. A few builders have gone to a fixed value resistor, bypassed, and some have used a gain pot on the second triode. I picked 1k with a 22uf and it works fine. For now it has no gain pot, if you use the volume control on the guitar, it cleans up nice. I was surprised by this, as that is how a Rangemaster works. It was still loud yet a lot cleaner. I have read you can use these with certain amps and other amps it will sound like crap. You can go from Bob Segar "turn the page" to Metallica's butchered version just by cranking the volume on the guitar. Ok, now the data, your results may vary. Input 70mv @1khz, volume max, tone max. Remember, your guitar can put out 1 or 2 volts, that's 2000mv. Some tube amp testers will use 100mv, or test at 400hz, to me that's fairly hot, i have settled at 70mv and use 1khz, i have seen how many amps and pedals will react to that, then i crank it up and see how much headroom there is and how the tone stack or controls work. You may be shocked, shocked i say at 40% distortion. My old Supro was over 70% cranked way up, think "Good times bad times" lead break dirt. 10% just starts to add some hair, 40% you can't play 7th chords and some minors and other stuff, they sound crappy. This circuit was designed for a 12AU7, the tube and it's variants does shine here. 5963, 6211, and 12AT7 was sounding good too. You can see the (relative) gains up and over 1000mv, that will nicely drive your amp into overdrive. You can only coax so much gain out of a tube, the distortion you can vary somewhat by going into non linear regions of the curves. But since this is starved plate design, all bets are off. 12ax7,5751 meh, either very clean or they had the distortion but the gain was gone, all the way up you lost signal compared to true bypass. Remember, this circuit was not designed to use a 12AX7 , so the low voltage shines with lower gain tubes and they actually blow away the 12ax7 in terms of output.