Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: AxeAmpTN on January 29, 2020, 11:57:56 pm
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Hey y'all!
A customer has come to me with another "attic" find. This time, a 1966 Champ. It is surprisingly clean (other than sticky-feeling tolex). Now there are several things wrong inside the chassis that I know will need to be addressed. The big question for me is the power transformer:
There is visible rust on the tranny, which I know can be an indication of problems inside the windings, etc. I haven't yet disconnected everything to test the voltages on the secondary, so I don't know how it will perform just yet. But for those of you with lots of experience on rusty transformers: do you have any advice going forward as I work on reviving this for my customer?
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Perform a test on the Transformer
if all is OK
Don't remove rust with abrasive paper or steel brush, clear (as possible) the rust with a rough cloth, then paint the transformer newly with a spray color
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in a far past laminations were exposed to weather as to have it rusty, the rusty acted as an insulation for the laminations, so, rust is not a big problem for lamination
Franco
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Don't remove rust with abrasive paper or steel brush, clear (as possible) the rust with a rough cloth, then paint the transformer newly with a spray color
+1
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So if the PT were bad, you'd throw the amp away?
Seems to me a Champ PT is readily available and not very expensive.
But that rust does not worry me. Anyway PTs can go bad without visible rust.
I don't even see the need to "disconnected everything" to test it. Start with a lamp-limiter, see if you get almost-right voltages inside. Smoke test a while, bypass lamp, let it cook for some hours. I say 9/10 chance it has some decades left. So get the blackest oil-base wood stain, rub over the rust, it will vanish.
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So if the PT were bad, you'd throw the amp away?
Seems to me a Champ PT is readily available and not very expensive.
But that rust does not worry me. Anyway PTs can go bad without visible rust.
I don't even see the need to "disconnected everything" to test it. Start with a lamp-limiter, see if you get almost-right voltages inside. Smoke test a while, bypass lamp, let it cook for some hours. I say 9/10 chance it has some decades left. So get the blackest oil-base wood stain, rub over the rust, it will vanish.
No, nothing's getting thrown away. Just looking for the best way to use what is here. In a worst case scenario, a transformer can be replaced.
I'm disconnecting everything because I know for sure the caps are 50+ years old and the previous owner bypassed the on/off switched and hotwired the 2-prong AC cord to the transformer. But as if that's not bad enough, the end of the cord is cracked or melted. Like I said, there is a lot that is wrong inside the chassis...I have a game plan for that, but trannys are not a strong part in my knowledge/experience base.
And thank you everyone for your advice on wiping/painting!
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I'm disconnecting everything
I would just pull the tubes.