Peavey Classic 30, crackle after warmup

[Doug]

Working on a Classic 30 that has a loud crackle/popping after warming up. Seems to be around bias supply or filtering end of the board. The amp really vibrates a lot, so I resoldered all the power resistor and filtering cap joints, maybe some improvement initially, took longer for the problem to occur. All connections look and test good. I can tap that end of the board and make it crackle. I can lightly tap the output tubes and trigger it as well. Tubes? Output transformer? Caps? Any ideas greatly appreciated.
Doug

[Amp Kat]

Tubes !

[Enzo]

Tubes! or the dreaded broken jumper wires.

Grasp each tube firmly with one hand - use a rag or glove if it is too hot for you. Now while holding it, rap on the side of it with a knuckle on the other hand. This tends to localize the vibration to the particular tube instead of hitting the chassis. ANy tubes respond with noise? Now wigle each tube in its socket. ANyone make more noise than the rest?

Inside the amp, the circuit board is divided into three sections, they form a U shape. Between the sections are a row of small bare wire jumpers connecting the sections together. From vibration, these sometimes break. WIth power off, get under each little jumper with something and gently tug on it. Any that come free were broken and need repair.

[Doug]

thanks guys, looks like tubes

Putting the amp through a workout, one tube failed, connecting plate to ground, through something like 47 ohms resistance. I've never seen a resistor so hot ( 390 ohm resistor between filter stages). Thanks again.
Would a tube tester have halped find this kind of problem?

[Enzo]

Perhaps, but in the trade, it is a whole lot faster to substitute a new tube in an amp to see if it was what it needed, than it is to get out the tester, set it up for the particular tube type, warm up the tube, and then test. And even then, most testers won't tell you if the tube is noisy, or microphonic, or lacking its tone.

Pops and crackles are a common sign of failing power tubes.