HI Vic; the cornvention is now in your back yard, instead of mine :-)
Concerning:
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?
In simpleton's words, the use of a small cap in series with a wire, just
like in series with an antenna element, raises it's resonant frequency. So
if done properly, can raise the resonance of the grid to ground connection
to above that of a single wire, for purposes of discouraging VHF parasitics.
Also can be viewed as a series-
resonant, low Z connection.
As for that Orr parallel resonant input circuit, that has baffled me too.
Could it be all wrong, and just acting as if it were not even present? Orr
has been wrong before, like about the folded monopole lowering ground
losses!
73, K6XK
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