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Old 7th November 2008, 02:38 AM   #1
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Default Guitar amp conversion

Hey guys,

A friend picked up a small homebrew SE tube amp on Ebay for cheap,and wants to convert it for use with his guitar.
It uses 6SK7 and 6AC7 tubes,with a SE 6V6 output.

Here's a rough schematic I've drawn up from looking at pic's of the amp:
Rough Schematic

Here are a few pics of the 'guts' under the chassis.
Pic 1
Pic 2
Pic 3

The OPT seems strange to me,I'm almost wondering if it is a push-pull transformer. No idea who made it,or it's impedance or anything.(I'll try to get the numbers,etc. from it,might provide a clue.) I guess for guitar duty,it doesn't matter a whole lot,as long as it sounds good.

So far he says the gain is too low for guitar use,but seems okay with line-level sources.
So,how might we go about getting the gain up? Fiddling some load resistors,etc? Any thoughts?

Thanks in advance!
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Old 7th November 2008, 03:16 AM   #2
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Join Date: Sep 2008
Maybe start by setting up the first stage like the original Fender Champ?
The 6SK7's grid is set up so that it won't cut off as much and distort. The 6SJ7's tube in the original Fender champ is normal cut off, so he may get some more favorable guitar distortion. The biggest factor will be that the 6SJ7 has higher gain, I think.

Alternatively, for the really classic and universally much loved classic champ circuit, he could go for the next major Champ revision. This is the one that became the classic studio amp for it's simple and great tone. Maybe this will give more mileage in terms of classic guitar tone:

Just some things to consider.

And yeah, weird output transformer... Must be meant for push pull?

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