[AMPS] Input Z

[measures]

>
>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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