[Collins] More on KWM-1 neutralization

[Dr. Gerald N. Johnson]

I don't recall saying unhook the filament, I meant plate and screen of 
the driver. The tube capacitances cold are not exactly the same as they 
are hot so the neutralization would not be perfect if done with a tube 
lacking heater power. Some would advocate using a dummy tube with a 
heater pin cut off, but neutralization is more picky than to allow using 
different tubes.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 5/23/2011 5:07 PM, AI2Q wrote:
> I'm happy to report that the neutralization of my venerable KWM-1 is now
> complete. For reference purposes, the PA neutralization was done
> according to the handbook procedure I have used for years on other rigs.
> My KWM-1 has a screen disable slide switch, so removing screen B+ is a
> snap. To remove plate B+ I simply unsoldered the B+ lead at the
> feedthrough bypass capacitor on the bulkhead near the rear-panel power /
> signal connector.
>
> Once B+ was removed, I peaked the rig's RF output into a 50-ohm dummy
> load using the pi-L controls and exciter tuning. The neutralization cap
> tweak gave a very deep dip on my scope connected across the load.
>
> I did try removing the filament lead from the 6CL6 driver tube, as
> suggested by KØCQ for the 32S-1, but this does not work in the KWM-1, as
> it disturbs the filament distribution for the remainder of the rig. As
> such, what I did was neutralize the driver with the 6146 screens off. It
> was very easy, at 28 Mc., to get a deep null from the driver plate
> neutralization cap.
>
> The so-called feedback neutralization was then accomplished by dipping
> the plate, with full B+ applied and grid drive, then adjusting the
> feedback cap so the grid current dipped at the same point as the plate
> current dipped. Bingo!
>
> Vy 73, AI2Q, Alex
> Member: ARRL, FOC, RSGB, CWops, QRP-L, Antique Wireless Association,
> Wide Area Amateur Radio Network
> http://home.roadrunner.com/~alexmm
>