Hi Glen
The bias pot has always been 5K on every PL board up to the S2 when they switched to a 1K and cost reduced the bias circuit.
Thank you Joe
so my curiosity got to me on this one
the total ohms resistance on a series two pl36 at the base of the bias transistor is about 1400 to 1500 ohms (with a fixed 680 ohm resistor and veri resistor). I measured your rev E board sitting on the bench and it was 2200 ohms (1000 fixed resistor and veri pot) to the base. Both boards have about .380 mv bias when running in the same backplane amp. Does running the opa134 verse the stock 351 have different out put to the pot?
I was going to try some Opa134 in the stock pl32 d500 board. I already reduced the stock fixed resistor in that circuit from 860 ohm to 680 ohm as used in the pl36 board. I guess putting a 5k or 2 k pot will give more range but could cause more heat in the pot as well.
well one more thing for discussion