BUZ901P BUZ906P replacements

[monto]

Imagining possibilities is endless, please post what problems your amp is actually showing today and we move from there on.

greets, I missed your post earlier for some reason
well I only mentioned about the mosfets because, due to the age of the amp and it is quite beaten up cosmetically, I think it may have exchanged hands many times, and it looks like some components were replaced/changed in the past, so I just wanted to make sure someone hadn't worked on it who perhaps made some mistakes (which of course could alter the sound, quality, long term reliability, etc)
I did hear from someone that the BUZ90xx power mosfets are not the original mosfets for the eighties sessionette 75 amplifier (model SG75), not that I know which mosfets it did originally use so anyways..

the amplifier issues, not too bad I would say. one of them is, the pots (originals) are in poor shape. I tried servisol super 10 on them, lots of it.. but it didn't really help. I've heard people say if servisol doesn't help you can open up the pots and actually give them a more intense manual clean (and slightly bend the contact arms so they make contact with fresh area of the conductive track inside the pots, so I might give that a go.. if I feel brave enough)
other issue with amplifier, it seems to cut out occasionally/lose lots of volume, and sometimes the distortion sounds a bit fuzzy/starved. I did clean all of the inputs with servisol super 10 especially the effects loop jacks, but it didn't fix the problem
the amplifier uses 3xTL072 and 1xTL071 opamps. I tried removing, cleaning then reseating the opamps but it didn't help with the unstable performance (sound) of the amplifier, so I ordered 4 new opamps off ebay as they are very cheap to buy so I figured I might as well replace them. they have not arrived yet though but should do in a few days.

[g1]

if you bought an amplifier from 1985 (ie. 30 years old), would you not change the 2 mosfets just for peace of mind so to speak (as it's hard to know how much use they have had in the past etc)

These are not a wearing part, and do not have a "lifespan" such as electrolytic capacitors do. Transistors are actually more likely to fail early on in their life. So statistically speaking, replacements may actually be more likely to fail than your originals.

[monto]

These are not a wearing part, and do not have a "lifespan" such as electrolytic capacitors do. Transistors are actually more likely to fail early on in their life. So statistically speaking, replacements may actually be more likely to fail than your originals.

great, that's good to know
ps. there's a bit of a fanbase for the award session sessionette amplifers from the eighties, they are really impressive for a solid state amplifier in my opinion. you do still see them cheap sometimes on gumtree or ebay etc. I was pleased to get one (model SG75 2x10) for under £100.
here's some reading about this amplifier if anyone is interested:
http://www.award-session.com/pdfs/SG...structions.pdf

[J M Fahey]

*EXCELLENT* amps

As of the originals, actual Mosfets used are even more obscure than you think, since not even the designer knew what they were.

Fact is, he chose to use some ILP prebuilt modules, on the idea that it would be easier for the end user to plain replace one such module, a chocolate bar sized block of U shaped aluminum rail filled with black epoxy, and only 5 terminals to solder: +V , -V , Input , Output , Ground , but one day ILP seems to have changed something and modules started dying often.

The designer had first to offer a self built replacement module and then a fully bipolar one, go figure.

I guess you have one of the house made replacements, still MosFet (which later became unobtainable).

Absolute worst case I guess you can adapt an LM3886 or TDA7294 chipamp there, probably drilling new mounting holes.