Guyatone amp issues

[CarlZ]

Hey all, I just got blessed with a Guyatone amplifier head from the early 70's. It appears to be pretty much a Fender Bandmaster clone plus or minus some loose change here and there.

Mechanically it's not in BAD shape. Cap job a few new switches etc are needed. The question is though, that I've never had to clean up an amp that had internals that were this dirty. There's what almost seems like an inch of dirt, dust, and general fung all over the boards and was wondering what's the best way anybody has found to clean up and get the nasty off of the electronics.

-Carl

[Chuck H]

Dishwasher.

Just kidding. The important things to remember are that any fluid cleaner is going to coagulate the "fung" such as it is. Use a toothbrush and Qtips to grind away as much dirt as possible before using any solvents (tip: Qtips can be purchaced in boxes of 500). Also, dust coagulated with solvents that has dried to form a paste can act remarkably like a resistor. This should mostly be a dry mechanical operation. Detail will be important. You don't want to create any continuity between junctions. Before you start, put a piece of masking tape over jack openings and pot cover gaps to avoid chunks getting inside. Resist the urge to use waterborne cleaning agents like 409 or Simple Green. They can damage some componants and leave behind residue. Do not use any solvents not intended for cleaning electronics because they can leave oily residue(dust collecting or at worst flammable). After you've finished any mechanical cleaning, if you have a compressor, use it. Otherwise get some air in a can. Then you can go to the solvents. Pay special attention to tube sockets and jacks. Clean pots with as little solvent as possible. Stay away from cloth covered wire with solvents. Stay away from transformer bell end or lead holes with solvents (dont get any cleaning agent into the transformer windings). Be sure the amp is dry before you try to fire it up.

I know there are a couple of DUH-HUR!?! kind of statements in there. No offense intended.

Chuck

[Don Moose]

A vacuum cleaner with a smallish brush attachment on the hose would be a good thing while doing what Chuck said. Get the fung the ... fung out of there and away from your valuable nose and eyes at the same time.

[CarlZ]

Oh well, guess there's no easy way to do it. I've got a small painters brush with the bristles taped that I normally use for dirty amps, and it generally works great but this is a whole new level of filthy. Seems the only thing between getting this sucker running again is all the dirt and a single broken plate resistor. And somebody was just going to throw it away! LOL

As an aside, after getting into the circuit a bit, it's a bit more Ampeg than Fender. Baxandall tone controls and that quirky pentod/triode in a single bottle tube, who's designation escapes me at the moment being used for reverb recovery. With a good amount of TLC this thing shows potential for being a really nice sounding amplifier.

-Carl

[Chuck H]

"I've got a small painters brush with the bristles taped that I normally use for dirty amps, and it generally works great"

I'm a painting contractor by day. So I have alot of old brushes...Often. Sometimes when I need a tool that can scrub and clean at the same time without a handle getting in the way I take a 1" paintbrush and hack off the bristles to about 3/4" long. I try to carve them off so they taper. That way I have a pointy center for fine edges and crannies. Works great. Just stiff enough to do some scrubbing and not too harsh on surfaces.

Chuck

[Alf]

Are these type of coupling caps in side ?


If so check them , mine were nearly all leaky !

Do you have a picture closeup of the inside ?

Alf

[CarlZ]

Yup those would be the caps this thing uses.

The chassis was a total bitch to get out. I thought the Ampeg Gemini was tough but this one...ARGHHH. The insides are an unusual mix of pcb and true point to point. The power amp section is completely hard wired, as are the tone controls and front panel switches. The preamp circuit is mounted on a smallish pcb with an attached emi shield.

I'm building final prototypes of a 2 channel and a 4 channel high gain amp design, along with working on some new transformers for those amps. So I've got a pretty full plate at the moment. But seeing as there's very little info on these things anywhere, I'll probably make a thread and post up some pics, a schematic, etc as time permits.

-Carl

[dai h.]

seems like most all of those Japanese oil caps ("CP" or "CP-C" marked) either are leaky or go leaky. If it's got old style micas I would check those and also the board as well ("tweed disease" check).

[Alf]

Dai,

It has got mica's in there can they be a problem too ?

I happen to have a softly creaking in ther which I though was an outputtube socket; if I touch it the crackle disappears.

Does it have enough outputpower ? I had to up a resistor somewhere at the end of the preamp to get loud enough.

Alf

[dai h.]

I think it is a possibility with old micas. It seems that some of the older casings which look like phenolic or perhaps other types of plastic did not keep out moisture as well as the modern epoxy coverings. Some from around the 60s have wax on them also.