Well, the new soup can 741 is in, and the volume is back. :thumb: However, it’s still very distorted. :angry: The volume and tone controls work, there is a big volume boost, and the sustain control seems to work. But it goes from ‘buzzy’ distorted to sounding like a broken transistor radio with no bottom end at all. I don’t believe this is how it is supposed to sound.
Should I think about swapping transistors? I can test them with a decent transistor tester. Hmm, maybe I will do that before I try and beg for some free advice. Or if anyone has other thoughts? Thanks.

Does anyone have a working pedal that can make a few voltage measurements? Knowing my luck, I put a good transistor back in lined up askew, so voltage measurements would tell me if everything else is OK and the 3080 is bad. Thanks.

Wow! Over a year later! I think I did ‘fix’ it, but it still isn’t a completely usable compressor. I found a soup can 741, and a 3080. I had to salvage a 3080 from a scrap board, but the leads were pretty short. So, I actually grafted on some leads with some solder and heat shrink tubing, and away I went. It actually works OK now. However, the ‘Sustain’ control goes from ‘a little too squishy’ to ‘waaaaay too squishy’. I haven’t figured out why. Some schematics show a resistor in series with the wiper of the Sustain control, so I’m experimenting with a value that will make happy. But since I have over a dozen compressor pedals, it isn’t high on my priority list.
All in all, it sounds clean and not too noisy. If I can tame the Sustain control (a different value control?), it will be quite usable.
For the tube unit, I’d check capacitors, and change tube(s). I don’t have that unit, so I can only guess. But start with capacitors and tubes. The schematic is actually out there, albeit with a caveat that it may contain errors. Still, you have an idea where to scope it, and figure it out.

If you have a scope and a signal generator, you can trace it and know where the signal gets mangled. Here is that schematic;

You can almost ‘undo’ the ‘Compress’ control and if you have four gain stages that amplify the signal, the problem is in the solid state section. Then you can try the TLO74, the transistors, or the 1N4148’s. It shouldn’t be too time consuming. Frustrating, sure, but even the shotgun method should have it figured out soon enough. Here is a page with a lot of internal pictures; http://analogguru.an.ohost.de/193/EH_Blackfinger-T_dissecting.html
You’ll get it, and learn a lot in the process.