Il giorno luned́ 15 aprile 2002 13:56:13 UTC+2, Jan Wemmel ha scritto:
Thank you very much to everybody who wrote a reply, it is good to see that
there is so much knowledge out there.
Even that I have been trained as a Radio and Television Technician in
Germany (admittedly 10years ago) and that I have a degree in IT and
Telecommunication, I have never seen a diode with varistor characteristics.
Unfortunately, the source for the part that Paul mentioned does not stock
the MA27A1, only the MA27A which is totally different. Panasonic in the US
offer the part via their website (http://www.pasc.panasonic.com) but this
service is not offered in Europe (UK), however the shop that Paul
recommended will get hold of the part from Panasonic. Do not try to get hold
of part from Panasonic directly in Europe a service manual would arrive in
6! weeks and would cost you £20+ VAT and postage (approx. $40). I got a
manual within 2!days from here http://www.divdev.fsnet.co.uk/man.htm. I can
only recommend the service!!!
Anyway, Goran was absolutely right, the Diode (varistor) controls the basis
voltage on a transistor (Q312) that controls the bias voltage of the amp.
Currently the transistor opens up completely and the transistor have the
full negative voltage (-53V) on their basis (not very good, luckily the
protection is VERY quick, I would be very upset to have seen my B&W speakers
go up in flames). I assume the diode has move the basis voltage of Q312 a
little causing the transistor to open up completely. However, I think there
is probably an additional problem because when I measure the resistance
against the chassis the right and left channel a completely different. Still
a lot of fun to be had... But I think the repair is still worth it as the
amp, even compared to todays amps still has some very good characteristics
and do you know of an end user amp that has two power supplies, one for each
channel (transformer, rectifier AND caps)?
Again thank you very much for your help!!
Jan
Hi, sorry for resuming a 13 years old thread.
I have a problem similar to Jan's. I did some research and found a possible replacement candidate fo the diode: Panasonic MA2B027 (datasheet here
http://www.datasheetarchive.com/dlma...SA-471901.pdf).
It seems there are several different versions of the diode (variants A/B, WA/WB, TA/TB, QA/QB). I think in my case the WA/WB variants are the correct ones (see also thread
http://www.audiokarma.org/forums/sho...99#post8216699)
BUT the part shows as discontinued in Panasonic website:
http://www.semicon..panasonic.co.jp/...0&part=MA2B027
Any idea for a replacement?
Thanks in advance