On Wed, Feb 12, 2025 at 03:12 AM, Jake KE8VGU wrote:
<Would that account for the filament transformer with no voltage on the center yellow tap that goes to the bias?
Yes !? ?At the junction of the plate and grid meter..... it goes off to the CT of the fil xfmr...(with the yellow stripe).? From there it goes out either side to the ends of the fil xfmr sec winding, then through the fil choke...and up to the tube socket? cathode pins 1 + 5.? ?Any bias is inserted in that CT lead....and also the bias cut off resistor.
On my L4B's? I used? 10 x 1N5408's? in series for bias....mounted on perf board.? ?That results in? 100ma idle current with 2650 vdc, and? 40 ma idle current in the 1900 vdc position.? ?You should have +7 vdc on the CT? with relay engaged, and? bias cut off resistor shunted.? ?On RX, you should have plenty of bias V, like aprx 35-50 vdc.
If that .82 ohm? HV fuse opened up.....? you would be reading zero volts for the HV meter.? ? With no B+ present, and drive applied, you will peg the grid meter with very little drive applied.?
You might also might have a grid to cathode short? on one or both tubes.? ?You could test the amp with one tube at a time (and temp block the empty socket so u don't lose airflow ).?
