[Hallicrafters] HT-32B

[Langston, Mike]

I have been working on a restoration of one of these for some time. The rectifiers have been solid stated and the 5V xfrmr leads isolated. HV measures 810v, LV is 308v and bias is currently set at -51v for my line voltage of 125vac.

Originally had no output which was traced to bad relay contacts affecting the driver stage. Replaced the relay and finally got some rf out, but only about 10 watts (cw on 80 mtrs into a dummy load). While tuning drive and output for peak (still at 10 watts), the 4A fuse gave way. I replaced the fuse, cut the rf gain all the way back and tried again while monitoring the plate voltage with a vtvm. In MOX position, 810v as before. However, now as I increase the rf gain and the finals try to make rf, the plate voltage drops to zero (and would blow the fuse again I'm sure if I am not quick with rf gain reduction).

I did the same exercise while monitoring the screen voltage on the finals. Starts at 205v but goes to zero as I increase the rf gain. I can do the same thing with the HV rectifier pulled while monitoring rf voltage at the grid of the finals. Driver tune and rf gain vary the rf from the driver as expected, and no fuse blowing with rf gain wide open.

I suspect I have a bad power xfrmr that provides 810v at no load but shorts to ground (probably through the 5v filament winding) as current flow increases.

Any thoughts and suggestions on how this can be confirmed would be appreciated. I had hoped the power xfrmr was good when I was able to get good plate voltage, but that was with no load.

Thanks for any help/suggestions.

Mike KL7CD