5f1 hum and squeal

[5thumbs]

I have a friend's 5f1 champ that he bought from a builder in NC. It has a lot of hum that gets louder as the volume is turned up and then develops into a squeal by 7-8 on the volume knob. Looking at the wiring, the builder has 100 ohm (not 100k) center tap resistors for the heater circuit grounded to the volume pot, and also has the 1st filter cap grounded their also. All of the grounds except for the green ac wire and red/yellow ptf wire are wired to the pot wiper with no brass grounding plate, the components are just directly mounted to the steel chassis. The input jacks and preamp bias resistors are run back to this point also. Before I go re-wiring the ground system with a buss, do you think it is bad grounding causing the problem or is their something else I need to check before I go to the hassle of rewiring all the grounds? I don't know if this amp ever played correctly or not since he has had it.

[Justin Thomas]

The heater center tap resistors SHOULD be 100 ohm, not 100k... I don't think you'd need to go so far as a buss. If it's in a 5F1 chassis, just copy what Fender did - I highly doubt a bazillion Champs have this issue... of course, if it's the same circuit in a different package... I find the filter cap being grounded at the volume pot (and the heater!) a little odd.

Tried new tubes?

Justin

[5thumbs]

Sorry Justin, I wrote that backwards they are 100k not 100 ohm. I am wiring the first filter cap to the transformer and ac ground and wiring the remaining grounds on a copper buss close to their circuit. I'll let you know what happens. I also will move the heater ground to ac chassis ground with 100 ohm resistors ;-)

[The Dude]

If not a grounding issue, I'd suspect a bad filter cap.

[Enzo]

Or a good filter cap with a poor ground connection, which might as well not be there then.