SAE A202 bias and DC offset adjustment?

[blhagstrom]

Does anyone KNOW the adjustments on an SAE A202?

I emailed the SAE guy, Jim for a SM, but never know if he's still around.

There ARE pots marked "offset" and "bias".
I assume offset can be read from the speaker terminals.

The outputs are 2SB755/2SD845, two sets per side.
The emitter resistor is a dual 0.27 ohm.
Checking the working side, I get about 27mv across both resistor halves together.
I replaced all the outputs on the other side. It had been hacked together once before. Managed to get outputs from China that appear OK.

I set the "new" side to 27mV and I'm running it watching for excessive heat.

 

[Binkman]

Hey there;

I dl'd the schematic and not much there. I did read that series of amp sounds better when you turn them off... (no b.s. I read that) German stuff with no idea the output in load? some weird 5-8.5 ohms? 12 14, 16?

This maybe one of those play it by ear deals. 10 a.m. on the volume is near or in the yellow zone? cut back the 27mv to 20? How does it sound? Not to clip it of course but seems like a conservative lower volume sweet spot at spin the wheel for speaker load. German amps do have design motif of sounding good at lower volumes and not meant to be cranked.

 

[blhagstrom]

Got the info. Posting to share for anyone in the future.

DC offset:

1) Connect 8 ohm dummy load to speaker 1 terminals.
2) Leave the inputs open
3) Turn it on, switch on speaker 1 and wait 3 minutes
4) Connect DMM to P14L (on main amp board, big wire connections) and chassis ground.
5) Adjust VR101L for 0V. (far rear input board)
6) Connect DMM to P14R (on main amp board, big wire connections) and chassis ground.
7) Adjust VR101R for 0V. (far rear input board)

Idle Current:

Connect DMM to emitter of Q205L and Q206L (the two pins on the big block resistor on the bottom end, R213L).
Adjust VR201L for 13.5mv +/- 3mv.

Connect DMM to emitter of Q205R and Q206R (the two pins on the big block resistor on the bottom end, R213R).
Adjust VR201L for 13.5mv +/- 3mv.

Now, if I can figure out what the bias diode is/was. She blew one. I made one from 4 diodes in series (1N4004). Seems "close enough"

The bias diode is 2438116100, SM shows it as RV DFV-312 AND BV-312. Neither of which shows up in the data sheet archive.