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"AB Systems" 1200 schematic

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nev23 View Drop Down
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Joined: 08 September 2008
Location: Taunton, UK
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    Posted: 04 February 2016 at 12:31pm
I've done  a major rebuild on this classic old beast from NYC.

One channel  had blown 7 output devices but amazingly nothing else. I've also replaced or mended the damaged switches in the frame. BUT the original RCA output transistors are long obsolete so I used modern MJ types. I swapped them around so I have a complete set on each rail of the amp: an MJ driver and original output devices on the negative rail and an original driver and MJ outputs on the positive rail. (the driver and output are exactly the same devices.) It works!

But there is a little oscillation near clipping on the positive swing. I did expect something like this as the new devices are so different to the old, particularly being faster.

Anybody got a diagram? It is the 1201 module; quasi-complimentary, 4 - 8 Ohm.
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