A few thoughts...
My first choice for set & forget biasing of Germanium circuits is to select the right transistor. Q1's bias depends mainly on leakage. Q2's leakage & hFE determine Q3's collector voltage. It's not about part number, it's about getting a tranny with the right specs. If you're serious about building Germanium pedals, then you'll need a bunch of Germanium transistors from which to choose. Different pedals need different specs.
My plan B is to select one of the base bias resistors for Q1 and Rc3b for setting Q3's bias. Resistor tweaking only works if Q1 and Q2 are already in the ballpark. You can tweak Q2's collector resistor, but it has the least amount of leverage.
FYI, the ratio Rc3a/Rc3b sets the max volume available.
I usually do all of that on a breadboard because it's easier & cleaner than temp installing stuff on a PCB.
Try disconnecting the ground from pin 1 on the PRE-GAIN pot and use a C-taper.
I have to agree with nearly everything
@Chuck D. Bones says here.
For the sake of posterity and giving my anecdotal experience, i'll add just a few caveats:
1.)
Set & Forget Using Transistors - This is viable option
with the right transistors. However, even the right transistors, or more succinctly, not enough of them, won't allow you to get a sustainably biased circuit.
For instance, I took a chance on a lot of OC75s to use in my TB MKII/Supafuzz excursions. After much swapping, I was not able to get the stock circuit to a point where it was not excessively gated. Granted, I don't have a huge stash of them so I am at the mercy of the 10 I have in my possession.
2.)
Set Bias by Changing Resistors - Combined with starting in the "Set & Forget" mindset, minor resistor tweaks can get you where you want to be but can't control for temperature induced leakage increases which may throw off the bias anyway. That's really the only reason I am in favor of a bias tweaking network composed of fixed resistors, trimmers, and an external "Bias Offset" control.
With that said, I agree wholeheartedly with what is written above. Just a few extra notes:
Q1b and Q2c Resistors - These are the values tweaked between the OC75 and OC81 equipped TB MK II/Supafuzz units. My personal preference is to tweak Q3c by altering Q2c and for the most part i have never had issues there.
Q3c Voltage Divider - I see many people tweak Rc3b and not lower Rc3a. In order to maintain the same bias characteristics when tuning Q3c with Q2c, youll need to lower Rc3a. If, however, you end up tweaking Rc3a directly with a trim pot, then this is less of a concern.
In my experience, the stock 470/8.2k string gives plenty of output volume. YMMV.
"Pre-Gain" vs. "Smooth"/"Clean" Control - I've tried the 250kA "Pre-Gain" (think Gagan "Easy Face"), as well as the 100kA "Smooth" control (think Fuzz Central "Axis Face") and the Fulltone/Analog Man 50k "Clean" control. I'm not sure which I like best. My poor memory says I liked the 50k "Clean" but i need to try them all out again.
One thing I'm certain of:
I love the MK II/Supafuzz circuit.