Lost Output on Princeton Reverb Clone

[Yemncsu]

**Resolved - details Below**

I recently completed a build of mojotone's PR kit(Schematic: https://bit.ly/2SSZ6Z9; Layout: https://bit.ly/37DNwoS). Initial testing seemed fine and it sounded great for several weeks. Recently I moved the amp to another location in the room(not the first time it was moved) and lost output. The pilot light, Rectifier and V6 still illuminate but all other tubes do not.

Initially, I wanted to test voltages on all filament pins(3.47 V to ground on each) and continuity between the filaments. Shortly after that, the 100 Ohm filament resistors sparked and popped. I'll be replacing those, but am looking for additional strategies to diagnose.

Initial reading looks like B+ shorting into the filament wiring on one of the power tubes might explain this. I dont see any obvious signs of that in terms of markings on the sockets or the tubes. I've tested resistance between pins 2 and 3 on both power tubes and get infinity. Testing between pins 2 and 3 on the sockets give odd results but center around .3M

I would appreciate any input and can provide photos if helpful. Apologies if I've missed any protocol with the post. Happy to update if needed.

Thanks,

[pompeiisneaks]

if you suspect a short, use your multimeter to test that none of the B+ nodes anywhere have continuity to ground.

Also if you're pretty confident you're not finding anything wrong, pull all the tubes and power it up w/o any tubes to see if you see anything misbehaving. You can also check all tubes for shorts between any other pin and the heaters (Heaters are always in 'continuity' due to being a strand that gets each side connected to heater power). I.e. in a 12AX7 you should have continuity between pins 4-9 and 5-9 and you should have a jumper between pints 4-5 so continuity there, everywhere else should NOT show continuity. For most (but not all) power tubes we use in guitar amps pints 2-7 are heaters, and they should be on the PR clone, it was 6V6's right? So pins 2-7 should have continuity but no others. I've had a fault where Pins 3 and 2 were shorted in a power tube and had the same failure, where it burned up my resistors and all the heaters in the amp

~Phil

[Yemncsu]

Thanks Phil! I now have a fully functional PR again.

I bought replacement 100 ohm resistors to replace the blown ones. While waiting checked that no B+ Nodes had continuity to ground which there wasnt. After pulling the tubes, I was not getting continuity between pins 2 and 3 on the V6 power tube or socket which i was expecting. I was, however, getting odd results between V5 and V6 as well as intermittent connectivity between V6 and all other filament pins through V1.

I replaced the resistors today and replaced the filament wiring from the lamp through V5 which cleared up the continuity issues. Went through startup process again and the amp was working. Must have been a cold solder joint on Pin 2 of V5 that lost physical connection when I moved the amp.

I think I likely shorted pin 2 to 3 on V6 with my probe in initial testing which blew the resistors so I think that was actually unrelated.

Thanks again,

Josh