Are you saying that when in USB or LSB, the minimum idle current is 160ma when you set the bias pot for minimum idle current and you have no mic connected? Etc.?
Yes, that sounds like massive under bias condition which can happen from numerous problems, such as:
one or both the power tubes are bad, the bias supply circuit is bad, the coupling capacitor from the output of the driver tube to the grids of the power tubes is bad or a component at the grids of the power tubes is shorted to ground or burned open, etc.?
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I’m assuming you know the high voltage rules and know what you are doing.
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So the first thing I would do is pull out the chassis from the case and remove the power tubes. ?Flip it over and from the bottom, visually inspect the power and driver tube circuitry for damaged parts.
Then when able to safely test the chassis, measure the actual negative bias voltage delivered to the power tube sockets when in SSB receive and then SSB transmit. The difference in negative bias voltage should be obvious between Rcv and Trx.
Receive bias voltage will be very deeply negative. ?
If it is there, replace the original coupling capacitor from the 12BY7 to the power tubes before going much further. It is the source of many of these power tubes issues. So is the small 1/2 watt, grid stopper resistor, which is connected to the coupling capacitor …. It is connected to the grids of the power tube sockets. ?
Also, consider joining the “Keeping The FT-101 Alive!” Facebook page for more help.
This group is only for these radios, none other. ?
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Bruce Collins