Greetings,
If a single-pentode linear like a Hallicrafters HT-33B has a gassy tube like a PL-172, will flipping the High Voltage switch on cause the Cathode Current to spike and throw the breaker a.k.a. the High Voltage switch back off? Or does that sound like something else? I tried leaving the filament on for 5 days.
I was excited to acquire a matched transmitter(exciter) Hallicrafters HT-32A and HT-33B linear amp (which could double for a deadman for a sea wall, and might). At some point years ago the former owner cleaned them up, replaced wiring, electrolytics caps and, as is common, swapped out a couple of the 33B's big, toasty rectifiers with ceramics. It then faithfully served as a phone patch to Antarctica with a beam atop a tall building.
Now, I partially disassembled them, dusted & reasonably cleaned everything, and found the 32A exciter to work CW wonderfully on 40m and to sound fantastic received on 10m via cross-country web sdr on SSB & AM.
The linear, however, immediately tried to peg (at least upwards of, if not all the way) the meter set to cathode current before throwing the internal breaker which flips the high voltage switch back off.
Mind you, the previous owner and a review online both cautioned me the glass tube PL-172 typically gets gassy "as evidenced by excessive plate current under all conditions" but is commonly getter-rejuvenated by keeping the filament switch on for up to a week before use. I did this for 5 days before testing (assuming the filament was really on just because the switch was up and the fan came on, and it doesn't have a bad filament transformer or something). I'm not really confident 48 more hours will do the trick.
Now, I do have THREE more PL-172's to try, so I guess I'm more fortunate to have them than unfortunate to have to leave each one filament-on, getter-basting for a week each before trying them one by one (the poor old fan).
If this cathode current meter-peg & breaker pop is symptomatic of a hopelessly gassy pentode, I'm stoked because one of the remaining 3 spares may rejuvenate. But if you can tell me it sounds more like a shorted transformer or something I'm less stoked.
Any insight on this is super appreciated!
Thank you
Jeff
If a single-pentode linear like a Hallicrafters HT-33B has a gassy tube like a PL-172, will flipping the High Voltage switch on cause the Cathode Current to spike and throw the breaker a.k.a. the High Voltage switch back off? Or does that sound like something else? I tried leaving the filament on for 5 days.
I was excited to acquire a matched transmitter(exciter) Hallicrafters HT-32A and HT-33B linear amp (which could double for a deadman for a sea wall, and might). At some point years ago the former owner cleaned them up, replaced wiring, electrolytics caps and, as is common, swapped out a couple of the 33B's big, toasty rectifiers with ceramics. It then faithfully served as a phone patch to Antarctica with a beam atop a tall building.
Now, I partially disassembled them, dusted & reasonably cleaned everything, and found the 32A exciter to work CW wonderfully on 40m and to sound fantastic received on 10m via cross-country web sdr on SSB & AM.
The linear, however, immediately tried to peg (at least upwards of, if not all the way) the meter set to cathode current before throwing the internal breaker which flips the high voltage switch back off.
Mind you, the previous owner and a review online both cautioned me the glass tube PL-172 typically gets gassy "as evidenced by excessive plate current under all conditions" but is commonly getter-rejuvenated by keeping the filament switch on for up to a week before use. I did this for 5 days before testing (assuming the filament was really on just because the switch was up and the fan came on, and it doesn't have a bad filament transformer or something). I'm not really confident 48 more hours will do the trick.
Now, I do have THREE more PL-172's to try, so I guess I'm more fortunate to have them than unfortunate to have to leave each one filament-on, getter-basting for a week each before trying them one by one (the poor old fan).
If this cathode current meter-peg & breaker pop is symptomatic of a hopelessly gassy pentode, I'm stoked because one of the remaining 3 spares may rejuvenate. But if you can tell me it sounds more like a shorted transformer or something I'm less stoked.
Any insight on this is super appreciated!
Thank you
Jeff