old amp ..easy..chep and work well

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I build this in 1990..my first amp....work well and sound nice too (1990 aspirations)
Exchange the parts (transistors) fo more modern types..

No need regulated power supply..
 

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tadiam said:
I build this in 1990..my first amp....work well and sound nice too (1990 aspirations)
Exchange the parts (transistors) fo more modern types..

No need regulated power supply..

No, exchange the parts for what you happen to have on hand. Very good first project - works without much fuss. I built something like this 25 yeras ago. The first project was an STK439, which is actually similar topology internally. Input and VAS polarities were swapped, but the same idea.
 
Re: re

tadiam said:
in the magazine say ....in class b....put more bias for class ab


Darlingtons have a nasty habit of running away if you put too much bias in it. The drivers get heated up when the outputs do, and there may not be enough thermal feedback to that BD139. If you do try to bias into AB, put the outputs right next to one another on the same heat sink, and mount the Vbe multiplier right to the case of one of the outputs. Might not be a problem with only a 40 volt rail, but some have tried to stretch that topology to 100W/ch or more and have trouble.
 
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