Smoking Resistor on Power Up

[Jim]

Hi, all. Just finished building my Percolator, and ran into an issue upon power up. The voltage at the IEC socket without switching on power was ~120V. The LED came on after switching on power. So far, so good. Then about 15 seconds later, resistor R13 (2K2 metal film) started smoking. I switched the power off at that point, and didn’t even get to checking voltages at the test points. The was a bit of static noise coming from the speaker, despite the volume knob being turned all the way down.

I’m not new to building (hand-wired) amplifiers or anything using PCBs, and the only time I had any issue like this was with a tweed Champ amp that I built awhile back. Cathode resistor in that case was smoking. I found the problem there to be that I had the output transformer wires swapped at the output jack. Slightly different problem, I know, but still involving the output tube (section).

I checked the PCB carefully for solder bridges, etc., and the wiring appears correct. It’s possible that I could have missed something.

Any ideas?

Thanks!

Cheers,
Jim

[brach]

Make sure all the tube pins are making good connection in their sockets. Sometimes it’s easy to over-loosen the sockets when assembling. If pin 2 (the plate) wasn’t making good connection then the screen (attached to the 2k2 resistor) would start drawing too much current. So tighten all the tube sockets.
…But I’d start by turning on the amp without the tube in the socket to see if the problem is just related to the tube and/or socket.
Keep me posted on what you find.
Good luck.
-Brach

[Jim]

Hi, Brach: Thanks for the help. Tightening the tube socket did the trick, and your explanation was very helpful! I was apparently a bit aggressive in loosening the sockets. All voltages within spec, and it sounds great through a 12″ Celestion Vintage 12 speaker!

Many thanks!

Cheers,

Jim

[brach]

That’s great!
Enjoy your Percolator!
-Brach

[Author]

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