Hi Brian, I hoped all your problems would be over when you replaced the coupling transformer, obviously there's still a problem. Don't feel too bad, the transformer did need replacing. The choke sounds like it's the original field coil from the old speaker, that's fine. It's still doing it's job as a choke, just not needed for the speaker magnet now.
The problem is still too much current being drawn, about 50% high and that's doubling the power dissipated in the choke. I hope the rectifier is still OK. You need to quickly take a couple more measurements to see what's drawing the current. Measure the cathode voltage pin 5 (should be about 22 volts, each plate pin 2 and the screen grid pin 3 of the 42 output tubes. The difference between the screen and each plate is the voltage drop across each half of the speaker transformer and will indicate the current drawn by each tube. If you measure the DC resistance (with no power) from the plate to screen then the current is the voltage drop divided by the resistance. That will show each tube's plate current and whether they are similar or one's drawing much more than the other. Then assuming that's where the current is going, if the cathode voltage is higher than normal that would be due to the excessive current but if it's low then that will be the cause, low bias voltage. Perhaps one of the tubes has a cathode to heater short or the cathode bypass capacitor may be shorted, the wrong cathode resistor or a wire shorting. It could be a bad tube, perhaps gassy. Is there a blue glow in one of the 42s? It may get worse after it's been on for a while. Have you replaced the electrolytic capacitors, they can go very leaky or even short right out. If they're the old ones it might have been one of them you heard the noise from. Before turning it on again, check there's no short developed across the B+ line, don't turn on if there is.
Do the checks and get back with what you've found, it's a bit tricky but you'll get there and have a fine set.
Don Black.
: I replaced that coupling coil in my GE M81 and wow what a difference. Voltage is gone from the grid of the one 42 output tubes completely. It sounds great, gave me a whole new perspective on keeping this radio. Brought B+ up a bit. Worked great for about 2 hours then I noticed that damn field coil getting very hot again?? Then I heard what sounded like arcing (I think from the rectifier) as the coil was burning hot by this time. I don't get it. I just replaced the filter caps. I just don't understand it. Does a 100 - 150V drop across the choke sound right. I think it is 450 on one side and 300 on the other now. The choke measures 1.2k. this all seems normal. What could possibly cause the choke to get burning hot. It was replaced by the guy my Dad bought it from, I guess when the original speaker went, he replaced it in order to use an 8 ohm permanent magnet speaker. Could it be maybee to low current rating?? It is a strange round looking choke. It looks like a small bell like the kind that you ring when you want service in a store. Maybee I should start looking at the resistor tolerences? They maybee adrift. Anyhow if any of this sounds strange to you please let me know. I am puzzled.
: Brian