In article , "David Farber" wrote:
GregS wrote:
Wondering if anyone is familiar with this series. I was
testing it out and the bias circuitry is not
functioning. There is shown on the schematic a bias transistor
along with one diode and pot.
There is no bias transistor on the two stages, just looks
like one diode. I intend on adding a diode or two to get it going.

There is a place on the boards for the transistor, but it was never
there.

greg

I found a service bulletin from 10/29/1975 that may or may not have an
effect on your problem. If your serial number is below US 7701 or Europe
51001, replace diode H720 and diode H721 with a 1S1555. When you say the
bias circuitry is not functioning, do you mean there is zero bias current?
It is supposed to be 10mv from TP701-TP702 and TP703-TP704.

Good luck.

H720 and H721 are for the bias of a couple stages back. I'll
check that out too.

greg