Ceriatone Forum

A while ago my 18w TMB stopped working. The sound went away gradually while playing it. An amp builder suggested the power valves, so I got new ones (It was about time, two years of playing it cranked). Nothing happened. I left it at a tech who said a resistor had come loose, and they fixed it. It worked for a week untill it started making very loud crackling noises, and the guitar cut in and out.

I've just opened her up to see if there's any loose resistors. There isn't so I fired her up in the hope she'd work again. Lots of crackling and the rectifier blew. Glowed whit hot and pour out smoke. Now it's black.

Is it as easy as getting a new rectifier valve, or is there an underlying problem that needs to be sorted out?

Cheers,
Al.

EDIT: The valve didn't turn black, that was just how the light was hitting it at the time.

There is sometimes a lot of drama when a tube fails catastrophically.   Fireworks, noises, etc.  So did the rectifier just blow or did something else take it out?  So put on your CSI cap.  I would pull all the tubes and with no power applied ohm out the high voltage caps and resistors in that part of the circuit.  Drain the electrolytic caps first.  Check for shorts or low ohmage across the filter capacitors and resistors that may be burned or out of tolerance.  If it looks good at this point put in the new rectifier (no other tubes) and check voltages.  They will read high without a load if all is normal.  Then install the remainer of the tubes and see if it functions OK.  Flakey power tubes could cause the rectifier to pull too much current and shorten its life.  Check for red plating in a dim light.  If something does look right stop and analyze, get a 2nd opinion, or ask a question.   I trust the tech that worked on the amp is competent.  Fresh power tubes could draw more power and stressing the old rectifier I suppose and hastened its failure.

I got someone to look at it in late January. Turned out to be a faulty power amp valve taking things out. The rectifier arced a bit, but the smoke was from the resistor over the filter cap.