Il giorno giovedì 21 maggio 2015 22:14:15 UTC+2, ha scritto:
Il giorno martedì 12 maggio 2015 18:58:39 UTC+2, Chuck ha scritto:
On Fri, 8 May 2015 12:39:15 -0700 (PDT), wrote:

MA27B1

Don't know of one, but this is the substitute that Panasonic
recommends.

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I ordered some MA2C029WA from ic-chips.com. We will see if it suits....
Quite pricey the expedition costs to Europe... not sure if it's worth but I'm sentimentally bound the my Technics. Probably a bad thing

I'l try with these you recommend if those I ordered turn to be a not suitable / bad replacement.

Best,
Marco

I now gained quite some more experience on the subject. I can confirm MA2C029WA are a suitable replacement for the MA27-A2. I tested that for years in "production" on my own Technics SU-V3 amp. Of course I can't guarantee about extreme conditions but it seems to me that the key function of "stabilization" is performed by the negative slope of the VF-Ta curve which would guarantee that, in the configuration in which the diodes are used, the lowering of VF with temperature increase will change the bias point of the circuit in a way that prevents thermal runaway.
The MA2C029 series offers a very wide range of forward voltages and it basically serves the case of "double diodes". I need to do more research if I had to replace the MA26 itself but I think the search for a replacement may be much easier for that one.

See this thread also: https://audiokarma.org/forums/index....ma26-2.621043/

Also some other hard to find diodes in these amps are the OA90 diodes. I was able to find some NOS on ebay at very reasonable prices and I stocked them up. See below for the datasheet.

Some technics amplifiers, for example the SU-8088, use the dreaded SVDSTV4HG.
Since that is attached to the heatsink with its very long leads (needs to be thermally coupled to the final transistors) it happens that sometimes the leads break because of mechanical stress and the bias circuit doesn't like that basically causing some cascade breakdown of the final stage.
See this dicussion
https://audiokarma.org/forums/index....-story.498025/


and also the datasheets:
https://www.alldatasheet.com/datashe...C/MA2B027.html
http://datasheet.octopart.com/MA26-P...eet-108588.pdf
https://www.alldatasheet.com/datashe...C/MA2C029.html
https://pdf1.alldatasheet.com/datash...ETC1/OA90.html (on the third page!)