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A mid 60's Epiphone comet guitar amp followed me home from the garage sales today. It has no speaker and I don't know if it was working before or not, but for $2 I decided to take it because the case is in good shape.
I have always wanted to look into repairing these things as I am always getting people asking me if I can work on them since I restore and build tube audio amps. I know there is quite a bit of help available on line and (I hope) here, but I never had a unit to actually work on until now. Is there a lot of difference between the two? Is this the right forum or would vintage forum be more appropiate?
Edits: 04/16/16 04/16/16 04/17/16Follow Ups:
I've always found the Telecaster Forum, to be VERY helpful with vintage guitar amps.
Steve
Thanks for all the tips guys! I Got home late last night and just read them. I appreciate the links and I will start checking things out using the schems.
I do not play so it is not likely I will be keeping it. My main goal is to see if I am interested/able to do simple trouble shooting and repairs on them as there are a lot of guitar players in my area. I will leave the mods to others.
I don't have a guitar at the moment; any tips on the best substitue for testing for now? I do have a signal generator. How about my audio preamp?
You have a signal generator and scope?
I find the guitar the best to test amp, at all volumes. One with single pole pickups, like a nice Telecaster or Strat. And one with humbucker pickups, like a Gibson Les Paul or 335.
Do you have photos of the transformers and speaker? Esp the manufacturer's stamped codes. These will help a lot, for dating the amp, seeing how OEM it is, and any upgrades or restorations needed.
Does the amp have single electrolytic caps or multi-cap can(s) in the main PSU?
A guitar is not an option I am afraid. What is the next best bet? I do have a 'scope.
I will post some pictures in a day or two.
Edits: 04/17/16
Do you have access to a microphone or electric organ or piano?A signal generator would be nice. At least, to check to see if the amp & speaker can make a nice sine wave tone. But, the SG won't help you check for complex overtones, overdrive, harmonics, saturation and all those other things that make a tube guitar amp sound so good.
Edits: 04/17/16
I think I will use my signal generator for the initial testing. Can I run music from my tube preamp to check out how it sounds?
Sure worth a try. Need to rig a 1/4-inch mono jack to the signal source. Never tried that setup, may sound a bit odd with the compressed nature of the music source & the EL84 guitar amp. And that narrow range onboard speaker.Maybe a nice acoustic guitar CD?
Edits: 04/17/16
"Acoustic guitar CD". Now that I have. Worth a try.
You may want to keep the amp original, or you may want to think of modding it. If you do, Robinette's site is a bit of a bible for Fender at least.
I have an old Selmer Trable 'n Bass amp, for instance, which I'm converting to a Fender Bassman.
If you have EL84 output tubes, 6V6 is probably a better sounding mod. And you can play around a lot with the tone stack.
vinnie2,
you can find the schematic for your amp on this site. Once you get it, just start checking around to see what needs fixed or replaced and you should be able to get the thing running again.
wishing you success. let us know how it goes.
roN
Is this it?
Vinnie...what little I know about guitar amps is that they are quite different from audio amps. First thing is that overdrive, and distortion are good in guitar amps. In other words early stages are designed so that they can drive the next stage into clipping.
Really clean guitar amps have a sound I can only describe as "campfire music". Also there are a lot of tone stacks built in that are typically absent in audio amps, and they have their own design and trouble shooting criteria, then of course there is reverb. Some power supplies in guitar amps sag, which is to say they are not real stiff supplies, that respond quickly to the various dynamics of the music. All these factors combine to give guitar amps their distinctive tone, as well as the usual suspects of different caps, tubes, and resistors imparting their own colors as well.
The guy that's way into this is FenderLover, maybe he can give you better insight.
twystd
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