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Old 25th May 2013, 01:10 PM   #1
Bando is offline Bando  Canada
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Join Date: May 2012
Location: Stoney Creek, ON
Default Got a HeathKit, now what to do?

Hello all,

I have recently acquired a heathkit aa-23 25 watt "hifi" amp. It sounds ok... but it is LOUD, way too loud.

I know it needs a single 1 meg pot. for the volume control (dirty). Its a mono block and listening in mono kind of sucks.

The tubes in order from input to output
6eu7 Westinghouse premium
6eu7 Daystrom
12au7 Daystrom
7591 Philips times 2.
rectifier tube is 5AR4 Westinghouse

To me there is way to much gain. As a Bass guitar amp it sounds nice with a EH 12at7 instead of the 12au7 (though still very loud). With it as a Bass guitar it sometimes "pops". I was thinking about splitting it in two and having a single 6eu7 feeding a 7591 in class A. Unfortunately the B+ voltage is quite high ~470 VDC and class A operation for 7591 is 300 VDC.

Sell, keep as Bass amp, or with less gain might sound better. Was originally used as PA amp for a Church.

James
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Old 25th May 2013, 05:10 PM   #2
lexx21 is offline lexx21  United States
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Join Date: Mar 2011
Location: North Carolina
You can use Deoxit to clean the pot unless you specifically want to replace it. Might be cheaper to do that if the pot is an Allen Bradley.

Have you replaced the electrolytic caps yet? You should do that first before doing anything else. After that, check your bias on the output tubes and see if those are in line with the Heathkit manual.

I would keep the thing if it were me, but that's just me.
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Old 25th May 2013, 05:37 PM   #3
rmyauck is offline rmyauck  Canada
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Join Date: Apr 2009
Yes, wise to recap it as you also risk the transformers, plus it will sound much better.

Hard to find 6EU7 tube sockets can be rewired to 12AX7 (In production and easy to find) which is basically the same tube with a different pinout.

I don't think HiFi amps were really designed for guitar (output transformers are different also) use so maybe get another AA-23 for stereo use and, maybe build a guitar amp.
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Old 26th May 2013, 12:49 AM   #4
lexx21 is offline lexx21  United States
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Join Date: Mar 2011
Location: North Carolina
Also if you have ceramic caps, get rid of those and replace them with something like poly caps. Ceramics do not make for good sounding caps in the audio path. There is a lot that you can do with this amp, and as rmyauck said, get another and then you will have a stereo setup.

Hifi amps, unlike guitar amps, are made to be linear. You can make this a good sounding hifi amp with a little work.
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