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HT-20 Harris B+ problem driving me nuts

J

jboydingram

1. B+ (PA) over load trips2. Pegged Plate current and voltage at plate onDisconnect B+ lead from power supply and supply operates OKChecked plate blocker, OKChecked RF bypass capacitors, OKChecked two known good tubes, Does not fix problem.So, power supply seems ok...appears to be a short somewhere in final but not tube, nor blocker. What am I overlooking? ThanksJ boyd
 
I'm assuming you're unhooking the HV at the ceramic insulator in the bottom of the tx, then the plate supply comes on Ok? If the plate VOLTAGE meter pegs, the HV metering divider board is likely shorted, which could also cause the high plate current indication, as the supply current is metered in the HV return circuit. I had a 25K do this to me years ago(same HV circuitry), and it took me several hours to find the culprit. Also, with the HV unhooked from the cabinet, turn the plate on and be sure you see at least several hundred volts of -grid bias on the multimeter. You probably know this, but if there's no bias, the tube will draw mucho plate current. You can also turn off the screen breaker, and see if you still get plate overloads.Good Luck with this! Gary
 
Right on, gary...it was an intermittent pot in the bias circuit...problem was under wiper arm and not visible. I appreciate thehelp...can you send me your e mail off list? I am [email protected]. Thanks....have a goodie for you....
 
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