The AM Forum

Since I got a rice box for an rf exciter, I pulled the 32v out of the rack and did some experiments with it.
It used to have a phase inverter circuit driving the grids of KT88 or KT90 tubes, with a D104 as a mic, and while it sounded ok, it looked BAD on the scope with audio tones.
I tried all sorts of changes and experiments and could not get it to work well, so as a test, I hooked up a 5000 ohm to 8 ohm transformer to drive the grids of the KT90 tubes.
It sounded good, but needed more screen voltage then 300 volts it was getting, so I upped it to 450 (three VR150 tubes).
Sounds much better, and wow does it modulate a LOT in the positive direction.
The mod monitor shows over 135% positive at 90%.
400 watts pep on the watt meter.
I am running the thing at 700 volts and 180 ma for about 90 watts out.

The KT90 tubes are likely in AB1, so its clean as the tubes will allow.
I think the KT88's sound better, but they are wide bottles and bump against the VR tubes I added.

The 32V3 is one I got a long time ago, I got two 32V's for $90.00, and rack mounted this one and gave the cabinet and driver transformer away to people who needed them.
Who knew they would be worth enough to pay for a nice vacation?