GAS son of ampzilla BIAS problem help needid

[MikeBettinger]

Mike,

Do you remember which main board used the Gas 100 IC?

I have a pair of 790001 driver boards and 790003 output boards sitting in a box.

I am thinking they need the MPQ6001 IC .

Hi Joe,

Looking at the schematics I have, the way to tell the difference between the bias circuits is: The GAS 100 IC has a single 250 ohm pot, while the GAS 100A has two 1k resistors as well as the 250 pot. Later versions changed to a 500 ohm pot to extend the adjustment range.

They shifted when they went to the 121B drive board which has the differentials in an IC socket, which is actually my favorite version of the Ampzilla.

Hopefully this helps. Mike.

 

[Burnedfingers]

Mike,

I'm totally confused now. My schematics are wet unfortunately and I can't make out a thing.

Looking at the board it looks like 500 ohm pot in series with a 1K resistor.

You wouldn't happen to have the output board schematic that you would share?

I must have the first version with the diff transistors soldered to the board without the socket. It has the wire jumpers which have also been cut. I assume they connect straight.

Joe

 

[MikeBettinger]

Joe,

I'll scan both bias circuits/output stages and post them, no problem. And yes the connections are straight across.

I can send you hard copies as well. I've been slowly trying to make good copies of some of my documentation, although, as usual I have so little time.

I'll try to scan these and send them in the morning.

Mike