> Since this thread started, I tried to locate the magic
> drive Z value with mixed bag and varied results. An
> amps member reported ~95 ohms for a single tube,
> a W6SAI Radio Handbook says ~160 ohms and now
> your 2 tube value. Someone has to have the real value,
> it's not listed anywhere in plain sight on the Eimac data
> sheet I just looked up on the web.
The Eimac data sheet for the 3CX800A7 gives 80 volts peak
rf cathode voltage and 36 watts of peak drive. The Svetlana
data sheet for the 3CX800A7 gives an input impedance of 54
Ohms. Since the data sheets for the 3CX400A7 show a very
similar ratio of peak cathode voltage (67 volts) and peak
drive (26 watts), I would expect the input impedance of
the 3CX400A7 to be very close to 54 Ohms.
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