Build Your Own Clone Message Board

How can I adjust the level of 'crunch' for the germanium boost? I would like to decrease it.

It's a little tough to do with this pcb. The best way I've found is to add a resistor in series with the input to knock down the input signal level. But with the toggle switch in the circuit, there's no good way to do it without signal leaking around the input resistor. You can try increasing the value of R11, but it's already biased pretty clean. What toggle switch setting do you usually use?

How about removing C10 and replacing it with another 47uF (or re-use C10) in series with a resistor - say a 330 ohms for starters?

This will maintain the DC bias conditions for that stage but reduce the gain so the stage wont distort so easily. Is that is what you want to do?
You would have to try different values of resistor to get the exact clip sensitivity you want - or fit a trimmer.

As it stands the gain of that germanium stage is governed mainly by the gain of that OC75 - anywhere from 60 to 130.

So if I insert a resistor (start with 330 ohms & work my way up) from the + leg of C10 to R11 would do it?

Yes that is the idea.

Without C10 present that stage would have a gain of roughly 10K / 3.9K or just under 3. With the 10uF cap present across the 3.9K at audio frequencies the 3.9K is effectively shorted out and the gain of the stage is determined by the gain of the transistor itself (with the cap in place changing the value of R11 will not change the gain, only the DC conditions). By adding a resistor in series with the 10uF the gain becomes roughly 10K divided by whatever resistor you choose (well the parallel value with R11). That's if I'm remembering all this stuff correctly.