Tube Amp Archive

Thanks to all. I'm strictly a hobbyist. Years ago good friend picked the amp out of someone's road-side trash and gave it to me, sans speakers, knobs and back panels, but otherwise in remarkable cosmetic condition. I have a '62 ES-345, and I want a stereo amp to go with it. They should make a nice s...

Thank you, Sluckey. Good tip, and good to know.

I am tinkering with a ~1967 Gibson GA79RVT stereo amp. The schematic shows the screen grids tied directly to the OPT center taps (there are two OPTs), with no screen resistors. The circuit in the amp matches the schematic. The schematic also says the screen grids should measure 322v and the plates 3...

Thanks, Stevem. I appreciate you going to the trouble of making the drawing/schematic - in color, no less. The problem was there was no connection between the negative of the top (red) cap and the positive of the bottom (black) cap.

Thank you, Martin. I followed your advice, got things sorted out, and put a jumper between the two eyelets at the top of the filter cap board. All is well. Strangely, there is no sign that a jumper was ever there.

I'm working on a '71 Bandmaster Reverb. Two leads from my multimeter are inserted in two eyelets on the filter cap board. The eyelet with the red probe is where the negative lead of one 70 mF cap goes; the eyelet with the black probe is where the positive lead of the second 70 mF lead goes. The two ...

A friend recently dropped off a Fender Bandmaster Reverb head for a checkup. All of the tubes are RCAs. The power tubes are 6L6GCs, both RCA, but one is taller than the other. The taller of the two has a small "FK" printed on the bottle; the shorter one has a small "CT." The internal construction ap...

Have you checked the filter caps? I worked on a 1967 Princeton Reverb that had a nasty hum in the reverb circuit. With the reverb control turned down there was no hum. When the reverb control was turned up, the hum started and increased the higher the control was set. I tried everything, and nothing...

AC ripple voltage? Never heard the term. Learn something new every day. I set the meter to AC voltage and put it between pin 1 (cathode) and chassis ground, right? What should I look for on the meter reading? Thanks, Stevem.

I checked the 220K resistor. The ground was good and it measured 230K. I replaced it with a new resistor anyway, rechecked the ground, and all seems to be in order. I checked for a continuous ground by touching one meter probe to the reverb output cable plug ground and the other to the input cable p...

The reverb/tremolo pedal and cables are long, long gone. One of the things I did while fooling with the amp was plug an RCA cable into the reverb pedal jack, and then shorted the other end of the cable - that is, I put a wire from the pin to the sleeve. The hum immediately stopped, but so did the re...

I'm working on a '67 Princeton Reverb that has a bad hum in the reverb circuit. I serviced the amp some time ago and all was well for about 6 months, then the hum started. With nothing plugged into the amp and the volume at zero and the reverb at zero, the amp is very quiet. Turning up the reverb kn...

Oops. No, Martin, I failed to check it with the intensity pot turned up. I'll try it ASAP, but I have a meeting tonight. Maybe tomorrow night. Thanks.

I checked the pot grounds as Martin suggested and everything seems fine. I've checked all the other grounds in the amp, too - no apparent problems. I turned the reverb to zero, and the amp still made that wretched buzzing distortion right at the beginning of a loudly played note or chord - mostly lo...

Thanks, xtian. I hooked the chassis up to a Fender Bassman cabinet that was about five or six feet away from the chassis and got the same problem. I knocked on the tubes and nothing untoward happened. I also retensioned the power tube sockets, which appear to be in fine shape, and gave them a thorou...