[Amps] Tune cap at minimum

[Jim Thomson]

Date: Thu, 3 Oct 2013 10:17:33 -0700
From: "Dave Hachadorian" <k6ll.dave at gmail.com>
To: <amps at contesting.com>
Subject: [Amps] 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 


## Spread the turns apart a bit.  Then the uh will be reduced.   Then you will need MORE tune and load C.
Your problem is you have too much uh on 21 mhz.   10m band is fine..so dont touch the 10m coil.
Just tweak the 15m coil very  slightly... not too much.   Just barely enough so it will tune.  

Jim  VE7RF