Gary Schafer wrote:
>
>> -----Original Message-----
>> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>> Behalf Of Roger D Johnson
>> Sent: Monday, January 23, 2006 1:07 PM
>> To: Vic K2VCO
>> Cc: amps@contesting.com; Tony King - W4ZT
>> Subject: Re: [Amps] Building or Buying a Tuned Input Network
>>
>> Vic K2VCO wrote:
>>
>>> Then, when you have designed or stolen the values, build the networks
>>> with mica compression trimmers for input capacitors, fixed silver mica
>>> capacitors for the outputs, and T68 size toroid cores.
>> I would recommend that the input capacitor be fixed as it set the Q
>> of the circuit. I'd put the trimmer on the output to compensate for
>> variations in circuit layout and tube input capacitance.
>>
>> 73, Roger
>>
>
> Having a fixed input cap and fixed inductance you can not vary the center
> frequency of the circuit.
>
> 73
> Gary K4FMX
If I remember my theory correctly, varying any of the pi network
elements changes both the center freq and impedance match. You
must have at least two elements variable to change CF and match
independently. As Vic said, these are low Q circuits and aren't
that touchy anyway. A purist could use both a slug tuned coil
and a trimmer cap.
73, Roger
--
Remember the USS Liberty (AGTR-5)
http://ussliberty.org/
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