[Collins] Now the tank circuit

[Dr. Gerald N. Johnson, electrical engineer]

Go to any 50 to 80 ARRL handbook. The coil taps will be described.
There's charts in one of the first chapters on computing coil
inductance.

Otherwise, to set up, connect a resistor from plate to ground of the
value you want for a plate load. Then set the tuning capacitor for the
prescribed value (all can be computed from curves or formulae in most
any ARRL or Bill Orr radio handbook). Looking at the output connector
with a SWR meter or antenna analyzer, adjust coil taps and load
capacitor for a match. You want a loaded Q of 12 to 15 to control
harmonics adequately. A loaded Q of 12 means the X of the input tuning C
is 1/12th (e.g. 1/Q) of the plate load R.

12BY7, 5763, 6CL6, 6AG7, all will drive the 6146 on the lower bands.
Might need a second such tube for high bands because of multiplying the
crystal frequency. The 5763 is more contemporary to the 6146 than the
12BY7 (TV vertical output, used in many ham rigs). Collins rigs use 6CL6
in some cases. 6AG7 is older, and there are dozens of other tubes that
would work, most any thing of the 6A6, 6F6, 6K6, 6L6, 6V6 family, except
maybe the 6G6 (a little wimpy).

Dual 365 pf BC cap probably isn't enough for 80 meters either. Use large
postage stamp micas, physically smaller capacitors can't carry the
current.

73, Jerry, K0CQ

-- 
Entire content copyright Dr. Gerald N. Johnson. Reproduction by
permission only.