Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: navdave on December 10, 2013, 12:15:05 pm
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Hello all I scored a fixer upper Evil Twin Amp on eBay with lots of corrosion and oxidation in it.
Is there a good product on the market I can use to clean the amp without damaging any components
or pc boards?
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Wow! That looks like it's been in salt water. Maybe Sandy? I don't see a quick clean up. That chassis should be stripped of all components. Too much damage to the board for me to tackle. All wires that I can see need to be replaced. Do the transformer wires look like that too?
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Not all the wires or components are like that. The power transformer and output transformer wires are good. Just some rust on the lams of both transformers.
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Start gentle and cheap. I'd hit it with 91% rubbing alcohol and a stiff brush of the type used to remove soldering flux. Thin metal tube squished onto 3/8" long black bristles about 3/8" long. Go for the stronger (91%) isopropyl alcohol vs the more normal 70%. If you can gather any crud together on the board, try to remove it with some Q-tips.
I am assuming that *you* are assuming that the solder joints are good and that the amp works (or you are ready to plug it in and see if it works...the lamp limiter is always a good bet on the first try)
DeOxit is the preferred item for cleaning pots, but it is expensive. I've had almost as good luck with regular Freon contact cleaner spray which is much cheaper. I would do just the board, first. See where you are in terms of go/no go.
It may be that you have to pay special attention to the 1/4" jacks. Treatment depends upon whether they are the black plastic enclosed type or open Switchcraft ones.
ed: I respectfully disagree w/Sluckey. It doesn't look that bad to me. It looks like atmospheric corrosion, not underwater corrosion. Yes, it's corroded, but inside all those wires the connections appear sound, at least as far as what you've pictured.
Tranny lamination rust = forget it until you assess further. Usually means nothing. But *do* use the lamp limiter on initial checkout in case you have something that's a catastrophic short.
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I overhauled a fender 75 that had more severe corrosion almost everywhere. Heavy rust is like cancer and will eventually eat the thing alive if you don't take thorough measures to remove the rust and protect the surface. Much like what sluckey said, the amp had to be torn down to just the chassis, the rust ground down, surface cleaned/ prepped, and hit it with black rustoleum over and over again. This stopped the spread and saved the chassis. There are some interesting websites describing electrolytic rust removal as well as chemical dips that can be done in lieu of grinding.
As for the boards, once I stripped and serviced the chassis I'd toss them in the trash and build in something more serviceable but that's just me...
Agreed, don't sweat the tranny rust.
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Thanks for all the advice fellas the only chassis rust is in one corner if the amp on the PT side. This thing sat in a garage in humid Alabama for who knows how long. I feel like dumping CLR into this thing but yeah that would be a mess. I have some 91% alcohol and a toothbrush I'm gonna hit it with tonight when I get off work.