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[AMPS] Tuned Input the rest of the question

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Subject: [AMPS] Tuned Input the rest of the question
From: (John Simmons)
Date: Fri, 07 Jul 2000 17:41:35 -0400
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Subject: Re: Tuned Input
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John Simmons wrote:

> I am new to this so hopefuly  I can pose a intelegent question  that
> some kind of answer.   Sence the thread seems to be running long the
> line of input matching I thought now would be a good time to pose this
> question.    I have recentley become intrested in trying  to building a
> HF amp using the russian gs-35b.  I have been told that the tube
> charistics are similar to the  3cx1500 (8877).     Based on the Arrl
> hand book  (76) construction artical the 8877 is quoted as having a
> chatode impedence fo 54 ohns.  I have not seen any Information on the
> GS-35b  that flatley states the chathode  impedence  for this tube is
> X.   I have looked through the handbook  to see if I could find a
> formula to calculate  the input impedence based on  bias  operating
> point or something similar to the formulas used to estimate the  plate
> load  resistance.   It would seem to me that there should  be some kind
> of relationship between bias , gain , drive level , input capitance or
> something which would give a clue as to where to estimat the input
> restistamce.    I know that  one of Wing field  programs gives a set of
> numbers for use of  a pi input network on  based on the expexted cathode
> resistance of  a triode.

I mashed send to soon !!!!!!!!
T he  question I am posing is there a way to estimate the cathode input
resistance .
I also noted that the 8877 has a indirectly heated cathode where it appears
from the schematic that the GS-35b  has the cathode tied to the heater
element.      I am making am making the asumption that instead of using a
transformer  heat connection as used in the 8877 I will need to use a
choked input to isolate the heater  transformer from rf input on the
The tube charistics can be viewed at
Any help would be greately appricaeate  as this looks like it might be a
great alternative to the $800 + bucks for a 8877.
de John Simmons KA4U


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