Fender Deluxe - feedback, hum & motor boating

[Mike9]

A guy dropped off his Fender Deluxe complaining about feedback. I fired it up tonight and one of the output tubes is glowing red hot, it has a terrible buzz and the bass pot is motorboating like crazy when turning it up. I poked each tube with a pencil and the hot one pops like crazy. I don't know how these are biased, but he said he replaced all the tubes himself. I'm going to check them against the suggested list, look at a schematic and go from there. Any other suggestions???

[slider313]

Looks like a full cap job is in order.I would also check the specs of all the resistors and check the coupling and tone caps for leaks.

[bob-i]

Sounds like you've lost the -bias voltage to that one tube. Fix that before you fire it up with tubes in there again. I'll bet 90% of the problems will be gone.

[Mike9]

I was thinking about that today Bob - I'll pull the chassis tonight when I get home. This amp is only a couple of years old it shouldn't need a cap job yet. I smelled a hot circuit last night so I'm going to look for that culprit first then check the -bias voltage. Maybe time for the college to order that Variac &7 Fluke DMM I've been talking about . . . I told them I need these to service the lighting system in the theater. ;)