| Tony, thanks for the help. I think that you have nailed the problem as an internal short in the power transformer. Measured at the rectifier tube socket pins 4 to 6 show 441 ohms through the secondary and only 1.4K to the chassis. Pins 1 to 8 show 17K to the chassis. I took the transformer covers off but didn't find any obvious problem. I spent the rest of the day looking for a B+ to chassis short but didn't find any. The strange thing about this is that I've never received even a tingle from handling the chassis. I'm using a Fluke digital multimeter with all the bells and whistles. It shows 256 VDC to the house ground at 413 MA and 121 VAC at 120 MA and a freq of 59.99 hz. I began to doubt my Fluke meter so I dug out an old RCA analog meter. It showed me the same voltages. I plan to press on tommorrow and start looking for a replacement transformer. Thanks again. ::I must have smoked too much pumpkin pie yesterday. If B+ were shorted to chassis we would have a short across the power supply output.
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::If the orientation of the AC plug makes a difference then I think that the primary and secondary of the power transformer are not isolated from one another. If it were simply a case of one side of the AC line being shorted to the chassis then I don't see how we would get the DC voltage with respect to ground. So, I vote for a primary to secondary short in the power transformer. Measure from the primary to each of the secondary windings.
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::: Measure resistance from rectifier filament to chassis. Should be at least 5 or 6K according to the schematic. If it's low, the filament winding might be shorted to the frame or the speaker output transformer might be shorted to frame. It could be in the transformers or in the wiring. I am assuming good caps since you recapped it and the radio plays OK with no ground.
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:::It's a sure bet that B+ is shorted to the chassis. All you have to do is find out where .
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:::Tony
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::::I've recapped it, replaced three missing tubes and repaired cracks in the speaker cone. It plays really well on all three bands. I did install the electrolytics correctly (not connected to chassis ground). However I can meter 256 volts DC on the chassis. If I ground the chassis it goes dead with the power plug in one way, and a very loud 60hz hum with it reversed. The 256 volts is present everywhere on the chassis, tuning capacitor, control shafts, etc. I've just started trouble shooting it. Does anyone have experience with this kind of problem? |
Will Hodges 
TonyC 