[MrFixr55]

Hi IntrStelle,

I was worrying about the output transformer more than the power transformer. When an output transformer has an open primary winding or if a radio is powered up without the output transformer connected but B+ applied to the screen (which will happen with an open output transformer), then instead of the plate dissipating all the current, the screen will. The screen is designed to handle about 2.5 - 5 mA, not 40-50 mA. Therefore, it heats up, burns out and touches the suppressor grid, essentially shorting B+ to chassis ground. This may be why your Candohm is toast.

Ohm your output transformer for open windings. If you find one, this may be the issue.

To test the power transformer, pull all the tubes and power up. The transformer should be cool to only slightly warm, even after an hour. If good so far, measure AC Voltage between the center tap and each leg of the HV winding. They should be equal. Finally, install all tubes except the rectifier. The transformer should stay cool to warm, not hot. Since the rectifier is not installed, you can do this test prior to finding the short.

If you find a short in the B+ circuit, first, pull the 2 41s. If the short goes away, there is your smoking gun (Oh well, the gun did not smoke but everything else did)
One mod that I perform is to put a 1N4007 diode in series between the power transformer and each plate of the rectifier. This should protect the transformer in case of a plate to cathode short. However, with a 6X5 type tube where the rectifier heater is powered from the same winding as the heaters for the rest of the tubes, this mod will not protect from a cathode to heater short. This is the reason why so many folks fuse the power transformer primary. You could get away with putting a fuse between the rectifier cathode and the input cap and field coil, but most "AGC" type fuses are rated only for 250V. You would want only a 1/5A fuse max. 1/10 A is probably enough.

Hope this helps!!