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Registered Member #3505
Joined: Sun Dec 12 2010, 06:03AM
Location: Albuquerque NM
Posts: 108
Thanks Herr but I already had the data sheets but they don't mention the plate material or acceptable coloration of the plate while operating which led me to start this thread.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
U4RIA -
Plate current is normally measured with an analog ammeter through the grounded center-tap on the LV secondary of the filament transformer, or through the "grounded" side of the HV DC supply.
Plate voltage is normally measured through a voltage divider using HV-rated resistors, drawing only a few MA.
Check out transmitter and HV DC power supply circuits in any of the ARRL manuals from the early '50's through late '60's for many examples of how plate current and voltage are monitored.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Dr. Spark: The problem is that plate voltage times cathode current does not equal plate dissipation. The usual efficiency of a properly tuned class-C oscillator is ~75%, so the product of Va*Ia might be up to 4 times higher than the actual plate dissipation.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Dr. kilovolt -
Common practice is to just directly monitor plate current, keeping it within the tube's maximum rating, and not try to "calculate" the power dissipated in the tube.
Here is a link to the RCA Transmitting Tube Manual TT-4 (1956). Figures 4-14 and 4-15 show power oscillator circuits for dielectric heating and induction heating, and show two different methods for metering plate current.
Registered Member #3505
Joined: Sun Dec 12 2010, 06:03AM
Location: Albuquerque NM
Posts: 108
There is a lot of interesting information on that site. As far as tuning goes on this VTTC I have the secondary res frequency measured at 409KHz and the primary at 379KHz. I read some where on this site that the primary needs to be around +0%/-10% of the secondary and its better to tune it a little low. Does this info sound correct or should I subtract a little on the primary cap to get the freq closer to 409KHz?
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4-125A VTTC
