I can't tell from the pictures... Are there any diodes thermally coupled to the outpt transistors?
We were trying to clone some of these puppies a while ago, but neither me nor the other person making them (I think it was either Rafael or Peter C) could keep them from overheating and blowing up...
Yes whole thing was thermally coupled. Transistors was glued to case
(alluminium box) and bias diodes are plased in close proximity.
I now have a copy of the original AES paper and it says something about clamping the output transistors with their biasing diodes (as opposed to with each other). I'll actually sit down and read it and I'll come back with more...
Yes, I have this paper too.
Opening the 990 was good lesson for me.
I did layout for Quad8 classic 10-transistor amp (like in ca137 card)
that fits 990 pinout, and had some strange problems with them.
At workbench, they runned pretty hot at +/-28 into 470 Ohm resistor
load for hours, and w/o heatsinks , very stable
with inductive/capacitance loads too,
however, placed into api'style classic micpre circuit, blew out each ~50's
time I switched phantom on, from maybe oscillation or some strange
issues caused by 48v-on spike...
I changed output transistors to mje 172/182, and did some layout
changes. Tested them today-seems OK
))
PS:
Nerd, nurd (noun, slang):
....
3. A Group DIY member
Hehe!!!!! Hi, nerds
)))
