I'm sure that this has been discussed and debated before, but here's about
2 cents worth:
As for those Eimac "Typical" ratings in the datasheets. I believe that
those are normally the result of one of two things. Perhaps folks at Eimac
had other approaches also, but my gut feeling was that they came up with
these numbers like this:
1) CPI/Eimac tested the tube in an amplifier, like the 4CX20,000A datasheet
tested at 98 MHz in their own cavity. The typical currents were read from
meters. These typical applications have a frequency quoted along with Pout,
Pin, etc.
2) Chaffee analysis (fourier series reconstruction of the DC currents using
the tube curves, a la Eimac tube computer #5). This is strictly a DC
analysis, so it neglects the RF effects such as ceramic heating, conductor
losses, electron transit effects at very high freq, etc. This is more
typical of how "Typical"
currents came about. It is usually stated "RF Amplifier Operation" and no
freq is given.
The grid dissipation is the important maximum rating to stay under. I'd be
surprised that there was a grid current limit as well, if the grid
dissipation max was quoted. Plate current is sometimes listed as a max
rating, only because it is closely related to max cathode current which is
limited by the cathode or filament emission.
John
K5PRO
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