Gibson GA-35 RVT Lancer has loud hum, low output, and nonfunctioning tremolo

[aaronlowther1993]

I snagged a 60's Gibson GA-35 RVT Lancer today for pocket change. On the upside the amp is super clean, and has a new Jensen speaker. And as with all such good deals, the amp has some issues. It powers on, and all tubes light up as they should. But as soon as the amp is taken off of standby, the power tubes turn blue. At the same time a loud hum, as if you were shorting a guitar cable against your thumb, comes through the speaker. This will happen even if all controls are on 0. If you plug in you will get some output, but not anywhere near what the amp should be producing. Here's a video of the phenomena.

 

[nasdak]

Classic check up !
Filter caps ; coupling cap ; cathode caps ; bias circuit....

 

[robrob]

Some power tubes will glow blue and not cause any problems. The tubes are a little gassy so electrons are hitting the gas molecules and causing them to glow.

That hum is so pronounced it may be caused by a loose ground wire causing a tube grid to float or you may just have a dying tube.

Here's my troubleshooting guide with a section dedicated to hum:

https://robrobinette.com/Tube_Guitar_Amp_Troubleshooting.htm

 

[corliss1]

I would recommend that amp get fully serviced before you turn it on again. That'll likely fix the issue and keep it going for another 40ish years

 

[TNO]

That's what they sound like when the original cardboard multi filter cap fails.

 

[slider313]

Yeah, filter cap hum.

 

[aaronlowther1993]

That's what they sound like when the original cardboard multi filter cap fails.

Inside of Gibson Lancer https://imgur.com/gallery/6ZQjC
I took some gut shots. Thought something might stand out.

 

[TNO]

Looks like the electrolytics may have been changed in the past though that doesn't mean they are still good. You might do a Google images search to get an idea if the caps are original or not. I think Rob may have called it with a bad ground connection somewhere.

The Kalamazoo amps from that time period use those orange drop caps and they are usually bad. There's a bunch of them in your amp.