[Amps] setting trimmer caps on amp RF in/out

[John Keating]

I'm looking for a procedure/recommendation on proper setting of the trimmer caps on the RF input and output of a QO HF 2000 amp. They are located right at the SO-239s. The input cap is in circuit (to ground) all the time; the output cap is in circuit (to ground) when the amp is not keyed (so the two are in parallel in that condition). I checked the input with the antenna analyzer and the output into 50 ohm dummy load, it's not wildly off 50 ohms across the HF band but it does vary -- 50 -j0 ohms at 4 MHZ, 51 +j4 ohms at 7MHZ, 56 +j5 ohms at 10MHZ, 60 +j0 ohms at 14MHZ, 58 -j8 ohms at 18MHz, 53 -j10 ohms at 21MHZ, and 43 -j4 ohms at 28MHZ. That makes the "bypass" condition SWR 1.25 in spots.

AI6LY