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Doxa 61 Amplifier
Doxa 61 Amplifier
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Old 15th July 2018, 09:51 PM   #1
Norgaard is offline Norgaard  Denmark
diyAudio Member
Join Date: Sep 2007
Location: Tjele
Default Doxa 61 Amplifier

I recently saw a photo supposedly with a Doxa type 61, or maybe a Doxa 61J/light
It appear to be based on the same 704 pcb which is used in the 70 Signature (mkII) version. This really put a spark to my curiosity, as it should be possible to upgrade to the rather expensive - and apparantly well renowned 61 from a 70 base.

Does anyone have a schematic of the 61, or would anyone be able to provide some closep's of the internals, to shed some light on the details.

I own both a 70SE and 70 sign. MkII - And in fact I also have two Audio 60 Dual Mono's which also branched into the Doxa 70 mkII, a rather overlooked but brilliant amplifier based on ultrafast NEC Ring-emitter power-bipolars. Completely different construction and topology compared the later 70B, 70SE, Signature etc.

These constructions are a mechanical nightmare, heat management is as poor as I have ever seen it and the workmanship... of course it might not all be down to how they were produced or modified (by Doxa) as both my later Doxa's have had (rather bad) repairs in the past - not surprising given the poor construction in regard to reliability.
I might later post some pictures to back up this statement, but the cooling paste seen on the pictures is something I added, none present from the start.
The thermal compensation TO92 were initially hovering over the "heat sinks" as well. Also notice that the emitters are the wrong value - could of course be a later repair. Photos are from the Signature MkII.

Fortunately/unfortunately when these amps are running correctly, they really perform, despite the flaws. So I really would be most thankful if anyone is able to send me a schematic by PM or other details, as transistor types used in the upgrade etc.

I'm about to further refurbish and mend the MkII anyway, so it's the right time for doing an upgrade to "61", or at least check out the feasibility of an upgrade.

Attachment: Layouter going bonanza?
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Last edited by Norgaard; 15th July 2018 at 11:05 PM. Reason: typos
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