Phonoland

Hi again,

I fixed my SHP3 amp, and it sounds wonderful!
I'm a bit puzzled with the bias measurements on my SHP3 Amplifier.
When I measure the voltage over the testpoint and the casing of the output transistors my DVM shows 0V.
When music is playing is shows me 0-20mv.

I found this advise from Tony Miller
"Actually, a better procedure is to measure voltages between the driver
bases on each channel, using a DVM, after about 15 minutes of
warm-up. Adjust the bias pots for 1.55 - 1.65 VDC. "

And this works like a charm!
I can set those voltages perfectly and the pots works great as well.

But still, no voltage on the testpoints.

So it looks as if the bias is not ok, but on the other hand I can perfectly set the base voltages.

Things I replaced in this Amp:

The output transistors 2n3055
Driver transistors Tip31C and Tip32C
4 resistors, I placed .22 Ohm not .2
Q5114 and Q5124 had already been replaced by someone, BC557B. The Hfe is not the same as I should have I think, perhaps this is causing the problem? What should these be replaced with?

All other reference voltages I see on the schematic match as well.

I hope some experience from someone can help me here

With kind regards,
William

William,
That method of biasing is one I, along with a couple other guys, developed. I have repaired "1000's" of them, never have checked the bias any other way--I slightly disagree with my late friend Tony--I adjust them when COLD. If the amp has the transistor bias circuit, I set it for 1.5 v. If the (late) thermal bias circuit, I set it for 1.7 v. Play a few selections at full volume--bias is fine if you can touch the outputs, without burning your finger---Ron Rich

Allright, I set the Bias like you said to 1.7V

Thank you!