Thanks to all who provided suggestions. As recommended, I
slightly spread out the turns on the 21 MHz inductor, and now the
amp tunes up perfectly, with the tune cap about 10% meshed.
Thanks again!
Dave Hachadorian, K6LL
Yuma, Arizona
-----Original Message-----
From: Dave Hachadorian
Sent: Thursday, October 03, 2013 10:17 AM
To: amps@contesting.com
Subject: Tune cap at minimum
I have an amplifier that tunes up on 21 MHz with the tune
capacitor at minimum value. It acts like the capacitance should
be even lower for max efficiency and output on 21 MHz. All of
the other bands, 10 through 160 are fine. The output network is
a pi-L, and the tubes are a pair of GU-74b's.
I was thinking of squeezing or spreading the coil turns on the 21
MHz inductor closest to the tube, but I can't find the dang
formulas to figure out which way to go.
Any ideas?
Many thanks.
Dave Hachadorian, K6LL
Yuma, Arizona
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