[Amps] HIGH INPUT SWR ON GI7-B AMP

[Steve London]

How did you determine the input impedance ? Tweaking or measurement ?

73,
Steve, N2IC

On 12/18/2019 12:29 PM, Bill McHugh wrote:
> Problem solved!  After much gnashing of teeth and scratching of head, I 
> discovered that the tube impedance of my GI7-Bs is actually closer to 150 ohms 
> per tube rather than the 100 ohms which everyone assumes it is.  The input pi 
> sections were assembled at the factory and installed with no regard for the fact 
> that the tubes had a different load impedance.  I wonder if someone decided that 
> the input SWR problem could be handled by running the radio's internal tuner?  
> As you know, doing that often causes the tuner to continually try to re-set 
> itself as SWR goes down, power out comes up as does SWR and so on.  It sure does 
> not work with my K3-perhaps some other radios with slower responding tuners 
> would find this an acceptable solution.
> 
> Some tweaking, mainly on the input C has enabled me to get input SWR on all 
> bands down pretty close to 1:1 or 1.2:1 in a couple of cases and my K3 is happy 
> once again!
> 
> 73 and Merry Christmas to all
> 
> Bill VE3NH.
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