[AMRadio] Globe Champion Neutralising

[Donald Chester]

In my homebrew rig, the grid coil is less that 18" from the plate coil.  I 
turned it 90 degrees, but maintained the same lengths on the leads from the 
ends of the coil to the split stator tuning cap.  14 mc/s and below, any 
capacitive unbalance will be insignificant with a nomal size grid coil.

You DON'T want to use the same lead lengths on the grids as you do the 
plates, to the tuning condensers.  The idea is to make any UHF/VHF self 
resonance in the grid circuit as far away in frequency from any in the plate 
circuit as possible.  If you use extremely short grid leads, use several 
inches of plate lead, or vice versa.  Another thing that helps is to use 
copper ribbon 1/3" to 1/2" wide, instead of wire, in all rf-carrying leads 
in the final. In my rig I had parasitics with the the split stator grid 
condenser grounded at the middle of the frame.  I changed to two ground 
leads, one at each end of the condenser each terminated at the same chassis 
point, and the parasitic went away.  On the plate condenser, I use two 
copper straps, one at each end of each section of the unit to go to the 
neutralising condenser.  I have parasitic chokes, wound over 10 watt 
noninductive resistors, in the grid leads of the final.  Every component in 
the stage should be grounded to a single common point on the chassis.  Each 
stage should have its own independent grounding point.  You want to avoid 
any common impedances between stages except of course the rf coupling 
circuitry.

I don't recall the issue, but there is an excellent article in an early 
issue of CQ magazine sometime shortly after WWII.  I think Bill Orr wrote 
it, but I'm not sure.  I got a lot of my ideas from the article, and they 
worked.  Otherwise, I never would have tamed that final.

Don K4KYV

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