I just added 160 to my 80/40/20 3CX3000A7 amp. It is configured as a Pi-L
for the upper bands but I switch the C2 to the other side of L2 for 160M
operation using a RB3 Relay. The relay also switches in an additional
1000pf. Really works great. I do have one problem however. I am using a
Amp Supply tuned input, one that I found at Dayton many yrs ago. I was able
to approximate the load of the tube by using a 50 ohm non-inductive resistor
and tuned the Arco caps for best match. This worked great on the upper
bands but the SWR on 160 is still at 2:1, which cuts back the output on my
Mark V. I assumed that the input impedance of the 3CX3000A7 is ±50 ohms. I
did not use a blacking cap for my calibration setup and don't think one
would be necessary. I merely hooked up the 50 resistor to the output of the
tuned circuit and fed power to the input and watched the SWR as I adjusted
the trimmers(one on each side of the toroid inductor). Any thoughts on what
I'm doing wrong? BTW, I left the tuned input in its final location under
the RF Deck for the calibration.
73 Bob W6TR
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