|Mr. Droopy-Drawers||Re: Have the pleasure to work on an AIMS Dual Twelve?|
I had heard a rumor that AIMS was started by a few ex-Fender employees back in the 1970's. Who know. But with the amplifier you have now, I would pull the output tubes, and try and measure the primary impedance. Put exactly 1VAC on the output jack, and measure the AC voltage between pin #3 of each output tube. You should get about 20-25VAC for an 8-ohm secondary, and about 30-35VAC for a 4-ohm secondary. If that checks, then you have troubles. The 75VAC at the grids; if this is grid-to-grid, that is plenty. I would measure Screen voltage, and then work on that output stage; check the tubes, check Plate current, Screen current. I know I get at least 90-watts from a pair of 6550's. That's using a 4K Plate-to-Plate OPT. If your B+ is up around 500VDC you too should be getting more than 50-watts from that amplifier. You either have parasitics, bad tubes, a blown Screen resistor, or a bad OPT.