[Amps] HIGH INPUT SWR ON GI7-B AMP
n2icarrl at gmail.com
Wed Dec 18 15:47:25 EST 2019
How did you determine the input impedance ? Tweaking or measurement ?
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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