Ampeg VT-60 head repair

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xtian
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Ampeg VT-60 head repair

Post by xtian »

Happy broken amp day! Here is an 80s Ampeg I picked up CHEEP. Has a toasted resistor in the power section--can't even read the value it's so carbonized. Hopefully I'll get a response from LOUD with the schematic.

Also, that cement resistor nestled in the filter caps has a fracture right in the middle. Prob should replace that, too.
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Firestorm
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Re: Ampeg VT-60 head repair

Post by Firestorm »

Can you tell why that resistor toasted?
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Reeltarded
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Re: Ampeg VT-60 head repair

Post by Reeltarded »

I dare you to mount it in a clear plexi head box....

Dare
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Structo
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Re: Ampeg VT-60 head repair

Post by Structo »

Too bad they didn't number the components on the PCB.....

I really hate seeing those tiny resistors in a tube amp.
Tom

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xtian
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Re: Ampeg VT-60 head repair

Post by xtian »

Structo wrote:Too bad they didn't number the components on the PCB.....

I really hate seeing those tiny resistors in a tube amp.
Right? Anyway, the one that blew was a 1w. But there are lots of 1.4 watt resistors on there, too.

Funny thing is that the head cab is overbuilt. Probably weighs more than the amp chassis itself!
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xtian
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Re: Ampeg VT-60 head repair

Post by xtian »

I pulled the scorched 820R in the photo above, metered it, and it reads exactly 820 ohm. Wow. Can a resistor be this badly burned and still operate properly? Or will it change value under load?
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Cliff Schecht
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Re: Ampeg VT-60 head repair

Post by Cliff Schecht »

Yes and yes. While it *could* be fine, it's usually good to replace suspect parts. If I can, I uprate burnt resistors a bit to try to prevent them from burning out again.
Cliff Schecht - Circuit P.I.
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Cygnus X1
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Re: Ampeg VT-60 head repair

Post by Cygnus X1 »

Cliff Schecht wrote:Yes and yes. While it *could* be fine, it's usually good to replace suspect parts. If I can, I uprate burnt resistors a bit to try to prevent them from burning out again.
Also I sometimes.
Other times a resistor acts as a fuse, saving other more expensive parts.

:)
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xtian
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Re: Ampeg VT-60 head repair

Post by xtian »

This is not the Ampeg, it's a cheap Fender PA amp which has been repaired before, obviously. I'm going to replace the two 5W power resistors with 10W versions. Photo is of the underside, where you can see the scorched board. How likely is this are to have become conductive? Should I be scraping around the traces, or is it not necessary?
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Re: Ampeg VT-60 head repair

Post by xtian »

Damn. These are some of the thinnest traces on the planet. I just lifted two of them. :evil:

And I keep putting my paws in the nasty heat sink paste. Damn!
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