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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hello, I got this vacuum tube, a GMI-32b, it's an indirectly heated tetrode to use in pulsed applications. The maximum ratings are 2 kW anode dissipation, 40 kV anode voltage, 100 A cathode pulsed current for a maximum duration of 10 microseconds.
Is this tube even suitable for continuous use? How should I derate it to use in a VTTC with halfwave doubled supply? Should I go for lower voltage, higher current - single parallel MOT bank doubled, peak supply voltage 5-6 kV, average anode current at most 2 A; or higher voltage - two series MOT banks doubled, peak voltage 10-12 kV, average anode current at most 1 A, or even a different voltage/current configuration? This, of course, assuming that the 2 kW anode dissipation is not exceeded.
Registered Member #1381
Joined: Fri Mar 07 2008, 05:24PM
Location: Hungary
Posts: 74
2kW Anode dissipation allows a massive power throughput, particular in a C-Class amplifier.
For CW it depends, if you can keep the tube "cool", via forced air or better yet somekind of liquid coolant/heat exchange system , (bulb and stem) than the real Anode dissipation is the "only" limit. Basicaly in this case the 270W heater and the electron clusters/currents, heat the entire tube (via thermic radiation & joule heating/friction ) Can't really guess the total heating (should take alot of calculations regarding, tube dimensions, heat sources and convection dynamics), so at these kW ranges just use as much cooling as feasible :)
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I know this tube must be cooled by forced air, at first I'll try a microwave fan (and another one directed at the seals) and monitor the temperature rise, if that won't be sufficient I'll use one of those "turbine" blowers.
I was just asking what voltage/current configuration would be best for cathode life; too high current damages an indirectly heated cathode by depleting the electron cloud and "ripping" electrons directly off the cathode; too high voltage on the other hand can poison the cathode with positive ions.
If no one has an idea, I'll try the two series doubled MOTs, as I think this tube might take high voltage a bit better than current in this case, as it is up to 40 kV dc rated.
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Derating a pulse tube to use in continuous TC duty
