[AMPS] more about the input swamp circuit

[Joe Subich, K4IK]

> 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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