[font=trebuchet ms]I'm a bit confused by your description. The only Ampeg I know of that had test points and adjustable bias was the original SVT head. I have a 1976 VT-22 (2x12") combo and a 1977 VT-40 (4x10") combo. Neither of these has any test points, and the only adjustment on the rear panel is a "Hum Balance" trim for the heater filaments. The bias is non-adjustable, other than by changing out one or more resistors to tweak the voltage divider circuit in the power supply. I installed multi-turn trimpots in both of my amps while I had them apart to replace the old electrolytic filter caps. Your amp may have been modded by a previous owner.

Have you had the chassis out of the cabinet? Most old Ampegs have a schematic pasted to the chassis cover, where you can't see it until you take the guts of the amp out of the box. On my VT's, the drawings are pasted to the cover which has the reverb tank bolted to it.

I don't have schematics for them that I can post, but Aspen Pitman's "The Tube Amp Book" has some for several different years and models.

You can also try the Discussion Board at the >Used Ampegs< website.

In my VT-22, I calculate the plate current by measuring the voltage drop across the 5 Ohm plate resistors. The VT-40 doesn't have any plate resistors, so I installed precision 1 Ohm resistors between the Cathode and Ground of each 7027A power tube.

Be very careful in there! Ampegs have very high (like 600 Volts!) plate voltages on the the power tubes. Even after turning the amp off, there can be enough stored charge on the caps to KILL you![/font] :eek: