[Collins] More on KWM-1 neutralization

Bob and Sue Jefferis ljranch2010-ham at yahoo.com
Tue May 31 18:58:01 EDT 2011


Interesting thread. Just catching up with mail after a holiday. As an addendum, I will pass this along: Some years ago I was given the opportunity to read and take some notes from a 1968 vintage Collins Production Test Procedure for the 32S-3. With respect to driver neutralization, they simply disabled the screen and of course, left the filament operating so the tube would have operational inter-electrode capacitances. Probably a good compromise between perfection and production efficiency.

73, Bob, KF6BC
On May 23, 2011, at 3:11 PM, Dr. Gerald N. Johnson wrote:

> 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
>> 
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