Getting back to the basics of troubleshooting. Blackstar content.

After the contretemps with the dual rectifier road king which has 33 knobs and 22 relays by actual count, I worked on a nice old Bassman on Sunday and Monday to level my alpha waves for the next migraine, which was a Blackstar HT60  combo with dead overdrive channels that I tackled today. The overdrive channels were noisy but took no signal and they expired completely on the bench with the occasional pfffft! pffffft!.

I remembered something about the clean channel being solid state and the overdrive channels being tube driven, so I started with a set of preamp tubes which changed nothing.

Getting back to basics I started with measuring plate voltages and wouldn't you know, there was very little voltage on pin 1 of V2 which receives its plate voltage through R41. The resistor tested OK with my extra high quality Harbor Fright multimeter although not so well with my ten buck analog multimeter.

But the voltage was going in but not coming out.

It was a simple enough matter to snip the resistor and sweat out the cut off stubs without removing the circuit board, check underneath with a mirror to see that all was well on the underside, and solder in a new resistor which I could do because the holes are plated through. Cleaning out the lead free solder from the holes and using some good Kester 44 did the job. To be on the safe side I resoldered pin 1 where it merges to the circuit board. It looked like it could use it.

The overdrive channels sprang to life with all the bowel loosening feces tone Blackstar is famous for, and after checking and adjusting the power tube bias, away it went. I kind of like the idea of a bias balance and level set which these amps have. I mean, I had to say something good about them, didn't I?

The point is, start  with the basics-swap out for a set of known good tubes and then some checking to see that voltage appears in all the right places. As it happened no fancy schmancy tooling or scopage was required to set this amp right, and it was not the first time I've seen such things happen.