Your PSU from AMI has 2x internal trimmers, Fil. 0-8vdc / B+ 116 - 120vdcSince I'm using a 'stock' AMI power supply, I haven't messed with the heater voltage at all--I tried building my own power supply based on the schematic, but I was in over my head once I got to the wiring stage.
Interesting! Hadn't heard of anyone using a PF86 in this circuit. I wonder if it's worth trying in my mic, considering I don't have the capability to adjust the PSU.