[Amps] HIGH INPUT SWR ON GI7-B AMP
magoo at isp.ca
Wed Dec 18 14:29:27 EST 2019
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
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