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From: Pete Brunelli
Date: Wed, 11 Sep 1996 14:46:13 -0400
Subject: Re: Champ tweaks?

At 08:19 AM 9/11/96 CDT, you wrote:
>I picked up a semi-operational clean blackface Vibro Champ at Pawn City. (It
>went something like: PS- Thats the only amp we got, sometimes it works,
>sometimes it don't. JR- What do you do to make it work? PS- I bump it (no
>effect) or hold the speaker wires like this (2 draw booms out). JR- Here's
the
>fourty bucks.)

James,
Good Price, but get someone to give it a quick once over if you are put off
on dealing with high voltage gear. The intermittant speaker connection can
fry the output transformer, and damage the final, probably a 6V6. Other
things like loose input connectors are usually a quick fix.

>My question is- Are there any worthwhile tube substitutions or other
>(preferably reversable) modifications to optimize for harp?

Most amps could use a retubing after a few years of hard use, maybe sooner.
Assuming that there are no problems with the rest of the amp, a new 12AX7
and a 6V6 will make a difference. The amp is biased for the 6V6 and i
wouldnt replace it unless i was going to do a complete overhaul. The champ
has a pretty small power transformer and the larger 6 series tubes like the
6L6GC and 5881 will not perform well. Transformer meltdown to follow.


BTW, the rectifier may be a 5Y3 tube, or it could be solid state. If it
isn't an obvious problem, dont mess with it.

the skinny: I wouldn't mod this amp, just retube and check a few tespoint
voltages, look for burned resistors, etc... Priority One = fix intermittant
speaker connection.

Pete
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Pete Brunelli p~onnix.com http://www.connix.com/~pcb