Just following the thread on the reflector.
>From the description it doesn't sound any different in principle to the
"supercathode" drive I was squawking about earlier this fall.
Supercathode: drive grid and cathode together, ground screen so Esc=-drive
voltage
G2DAF: drive grid and screen together, but multiply screen up. Esc=k*drive
voltage
Now I don't have any original G2DAF literature, but by the above (and only
that) I have no difficulty believing the linearity claims of G2DAF...Eimac
themselves measured IM3 products on the order of -40dB or better with the
supercathode drive technique.
I tried to calc out the supercathode drive with larger tetrodes and, as it
turns out, there wasn't enough power gain in the "pure" connection to make
it feasible.
But I suppose the use of a multiplier stage--which adds another "degree of
freedom" to the design--would really help the drive requirement. My
difficulty with supercathode was that the peak drive has to be at or above
the rated screen voltage, usually a pretty hefty drive level into 50 ohms.
But the ability to multiply it would solve that problem...
I guess the point is...Eimac themselves have published a circuit
configuration where screen voltage is not constant, that yields excellent
linearity. So by itself that isn't sufficient reason to dismiss the G2DAF.
Could anyone be so kind as to supply lit. references so I can become better
educated? Thanks!
------------
Scott Townley
nx7u@primenet.com
------------
Collector of:
Stoddard Aircraft EMI/RFI receivers and accessories
Big Parts for that Big Linear Amp
70's era RF test equipment HP/GR/Tek
Radio-related technical reference material 1940+
...anything else that will keep me off the streets at night
--
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