Several months ago I inquired about a problem with my 4CX1500B 160-10m amplifier. The initial symptom was a welded vacuum relay while operating on 12 meters. I replaced the relay and subsequently dis
This is rare but does happen. There can either be a feedback path that causes the problem due to the fact that by-pass capacitors are chosen to bypass HF RF not low frequencies or the tetrode at time
Paul, your case with that amplifier is interesting. Could it be that your plate choke was arcing over between those turns where the insulation flaked off? Or perhaps those turns tended to get shorted
That is what worries me. I wonder it it was on the edge of instability all along until a minor change in the plate choke pushed it over the edge. I wonder if I should think about upgrading the by-pas
Manfred, Thanks for the reply. Could it be that your plate choke was arcing over between those turns where the insulation flaked off? Or perhaps those turns tended to get shorted via creepage over th
Paul, 1000pF is 45 ohms at 3.5 MHz. If the plate choke is 250 microhenry - typical value - that's 5500 ohms. There's around 2kV RMS of RF on the plate, so that's 360mA of RF in the choke and 16 volts
Paul, 1000pF is 45 ohms at 3.5 MHz. If the plate choke is 250 microhenry - typical value - that's 5500 ohms. There's around 2kV RMS of RF on the plate, so that's 360mA of RF in the choke and 16 volts
Paul, 1000pF is 45 ohms at 3.5 MHz. If the plate choke is 250 microhenry - typical value - that's 5500 ohms. There's around 2kV RMS of RF on the plate, so that's 360mA of RF in the choke and 16 volts
The Ameritron choke is 225uH and most others are a lot less going as low as 50uH in the SB-200/220 amps. In those cases the choke becomes part of the output network. I always suggest a .0047 at the b
Paul, Which leaves me wondering if other upgrades or changes would be a good idea. The by-pass capacitors surely are not much good at low frequencies, some maybe even a bit marginal on the lower HF b
Paul, 1000pF is 45 ohms at 3.5 MHz. If the plate choke is 250 microhenry - typical value - that's 5500 ohms. There's around 2kV RMS of RF on the plate, so that's 360mA of RF in the choke and 16 volts
Manfred, Thanks for the work and reply on analyzing my problem! Sorry I got behind on correspondence this week. Now I'm catching up. From the number of turns, length of the winding, and the dimension