Hey all!
Been browsing the web and seen that you guys seem pretty knowledgeable, so I have a few questions I hope you can help with. I recently bought a '76 Pro reverb not knowing if it worked at all because it was missing the 2 gl6's. Eager to try it out, I went to guitar center and all they had was a pair of Groove Tubes, so I got them and fired it up. Anyway, the amp seems okay aside from a few issues that hopefully are minor to repair. I think it may need a new reverb tube, because it buzzes loudly when the reverb is turned up. I also shorted an RCA cable to the vibrato effect to engage it, and all I get is a ticking sound that responds to the controls. If the amp is left on for 20 min or so, it will start humming like there is a bad ground, so maybe check solder joints? I've opened it up and all seems original including the RCA tubes, so they probably need replacing. Also, the reverb tank is missing one of the pins that connect the springs (although it sometimes functions) and I was wondering if anyone knew if there's a place where it could be serviced. Overall, seems to be working alright besides these problems. Haven't checked solder joints yet, but will do soon. Also, does anyone know how to bias the tubes on this amp? I only see one pot by the power tubes. I have a multimeter, but I have no idea what to do with it as far as biasing.

Thanks Guys!!!

There is no adjustable bias in that platform -- only a "hum balance" control (which possibly may need an adjustment). Reverb tanks are cheap enough, you're better off replacing it. Likely, your pre-amp tubes are tired and due for a change as well. Frankly I'd doubt that there are any soldering-joint issues since this amp was built well before the era of "RoHS". The periodic hum is probably indicative of aging caps (both filter and bias) that are ready to give up the ghost. I'd find an amp tech qualified in older tube Fender architecture and let him run a full diagnostic bench-check on it. Repair and/or recondition whatever is required and you'll have a sonic friend for life.

Best of luck, HTH

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY

+1 on Arjay's advice.
don't mess with the solder joints,especially if you have never been inside a chassis poking around....if you have,then you should know how to keep from being BBQ'd.
I have a '66 Pro Reverb,it's a fantastic sounding amp.
good luck!

+1

AA165 = The Holy Grail

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY

Hey guys! Thanks for your input. Sorry for the late post. Been busy with that work crap. Anyways, I pulled the tubes in the preamp section 1 by 1 (of course powering down while I did it) just to see what did what. I noticed that the amp will still function with a couple of the tubes pulled. I believe that one is reverb return or something? Anyways, the vibrato still doesn't function, but, the buzz has dissapeared! Leading me to believe that there was a dirty contact somewhere in one of the tube sockets. My question now is does anyone know of a good contact cleaner for this and how would I do it. Thanks arjay for your advice. I still want to have a tech go through it when money and time allows. Also, are you saying that the tubes can't be biased at all? I've read on other sites that what you refer to as the hum balancer is indeed a bias pot. I don't know; seems to be a lot of self proclaimed experts out there and every one contradicts another. If anyone knows about the tremelo circuit that would also be appreciated. Thanks again guys! You've already been a big help