Tweet
Got this thing on the bench and man is it a HEAVY combo! Complaint is no output so pulled the chassis and found both 1A +/-23v supply fuses blown. Popped in new fuses, put on the dim bulb and it fired up. The bulb dimmed as it should so I swapped over to the variac and all looks good, only pulling about 750ma out of standby. I shutdown and threw the bias probe on it and I got about 17ma on both tubes (read that these run cold) so that tells me the tubes are biasing. I have my lights on the front panel so everything in the 23V circuit seems to be working as it should. Suspecting maybe a intermittent short in a power tube I threw those on my hickock and let them burn for a bit, I tap the tubes hoping one will flash but no shorts. Tubes are used (3100 out 5000) but they still have some life in them. Next I inspected for any bad solder joints (that I can see) and all looks good. Checked the 23V supply on both sides of the molex and it is rock solid. Checked ESR on the caps and found nothing wrong there. At this point I put the amp back together and cranked it. Sounds glorious! I can't see/hear anything wrong with this amp. The only thing I couldn't properly test was the foot switch circuit as the switch wasn't included but the channel switching button on the front panel works fine.
I hate these situations as there is no smoking gun and I really don't know what to tell the customer. How do you all handle this? Something I am missing?
I attached a screenshot of the 23v supply and the footswitch circuit. I did notice +23V ties to the filament through R107, looks like they are elevating the filament lines. I guess it is possible a quick filament short took out both fuses? Feels like I am reaching on that one a little..
I hate these situations as there is no smoking gun and I really don't know what to tell the customer. How do you all handle this? Something I am missing?
I attached a screenshot of the 23v supply and the footswitch circuit. I did notice +23V ties to the filament through R107, looks like they are elevating the filament lines. I guess it is possible a quick filament short took out both fuses? Feels like I am reaching on that one a little..
Comment