>
>Thanks Rich. Here's where I display my stupidity... I was going to avoid
>a swamping R type of input circuit. But I suppose for a sand-state exciter
>the swamping R presents a more stable load - is this true?
>
Quite true, Bill. The grid is virtually an open circuit, so the exciter
needs a termination to keep it from shutting down. Provided that it is
installed very close to the grid, the grid-term. R also swamps the vhf
damped-wave signal that is fed back from the anode-resonant circuit to
the grid by the tube's built in feedthrough capacitance. .This reduces
VHF-gain
cheers.
>----- Original Message -----
>From: measures <2@vc.net>
>To: Bill Coleman <n2bc@stny.rr.com>; AMPS <amps@contesting.com>
>Sent: Sunday, February 27, 2000 11:20 PM
>Subject: Re: [AMPS] Input Z
>
>
>> >
>> >How do I determine / where can look up the input impedance for grid
>driven
>> >tetrodes? I'm not satisfied with the input circuit I have in there now
>and
>> >want to give it another try.
>> >
>> In Class AB1, input Z is essentially the reactance of the grid-C plus
>> the grid-termination resistance. The practical choices of grid term. R
>> are 12.5-ohms (4:1 bifilar transformer), 50-ohms (direct), 200-ohms (1:4
>> bifilar transformer) and 450-ohms (1:9 trifilar transformer).
>>
>> cheers, Bill
>
>
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>
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