>
>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?
>
? My guess is that the idea was to increase the grounded grid-resonance
(by cancelling some ot the internal L) in order to increase vhf
stability. In practice, it increases the resonance, but only slightly.
. . Some say adding C was done to lower IMD, however, since a stock
3-500Z is already far cleaner than the best transceiver, this doesn't
make sense to me.
>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).
? A parallel-tuned circuit is undoubtedly Not a substitute for a
pi-network. .It is my opinion that an amp-guy worth his salt knows the
reasons why.
- In 1990, Bill Orr wrote a letter to QST complaining that a QST article
contained 'numerous technical errors' without giving any references.
QST-staffer Dave Newkirk said Orr's letter was evaluated as a "zero"
because he failed to give any example of an alleged technical error..
> 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?
>
? somewhat unwell
>I had a good time yesterday at the DX convention, looking at the innards
>of the Alpha and Henry amps. Nice work.
>
? Nice looks are not necessarily wonderful in the long haul. This
applies pretty much equally to cars, amplifiers and women.
- cheers, Vic
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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