[Collins] More on KWM-1 neutralization

[AI2Q]

Mea culpa. I didn't want to imply that you advised removing the filament 
voltage Jerry. What I meant to say was that the 32S-1 procedure calls for 
that step!

Thanks for all your assistance and speedy replies.

Vy 73, AI2Q Alex


----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at weather.net>
To: "AI2Q" <ai2q at roadrunner.com>
Cc: <collins at mailman.qth.net>; <kwm-1 at yahoogroups.com>
Sent: Monday, May 23, 2011 6:11 PM
Subject: Re: More on KWM-1 neutralization


>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
>>