In planning my 2 x 3-500z gg amp, I've been looking at schematics of similar
units, and there are a couple of questions that have arisen:
1) Some of them do not ground the grids directly, but do so thru a bypassed
choke or resistor. Why?
2) Some of them use the usual pi-network input circuit, but others have just a
parallel-tuned circuit (the Bill Orr handbook, for example). I know that the
input impedance of the pair of tubes is quite close to 50 ohms, so the impedance
matching function of the pi is not needed, so I guess the circuit is used just
to provide a 'flywheel' and a return path for the RF plate current. But wouldn't
a parallel-tuned circuit have a relatively very high impedance compared to the
load provided by the tubes? How does this work?
I had a good time yesterday at the DX convention, looking at the innards of the
Alpha and Henry amps. Nice work.
73,
Vic, K2VCO
Fresno CA
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