[Collins] KWM-1 neutralization procedure
AI2Q
ai2q at roadrunner.com
Sat May 21 18:56:42 EDT 2011
Yup. Much as I thought, Jerry. But, the RCA jack is marked PA GRID, so I
will trace it out and hopefully report to the reflector.
Tracing the circuitry in this rig is not easy, by the way, but it is what I
had to do to troubleshoot it. In some cases, replacing components is more
difficult than locating them, too! It's obvious Collins designed the rig to
be wired in layers when in production.
My PA neutralizing cap is a ceramic trimmer, not an air variable. It is
located on the underside of the chassis. The feedback and driver caps are
also ceramic trimmers, but located topside.
BTW, I just signed off with EI7JN on 20 meters, and he said the "ol' gal"
(his words for the KWM-1) sounded better in Dublin than most rigs he hears.
I haven't tried CW yet.
I have another observation and query. The power supply HV choke is shunted
by a 0.05 uF bathtub cap, which was shorted. A mica replacement I installed
also shorted after a while. At the moment I am running without the cap
across the filter choke. In any case, I calculated the resonant frequency of
this cap and the 8 Hy choke it shunts, and I don't see what good it does, as
the calculated frequency was about 250 Hz. Any thoughts? A second harmonic
high-Z filter of the DC rectifier frequency, perhaps? The later power
supplies, for the KWM-2, have a more elaborate ripple filtering scheme. In
any case, I need a 0.05 uF bathtub if anyone has one to spare.
Lastly, my pal AA1CA was a U-2 pilot. Tom was a colleague of Francis Gary
Powers. He wrote me an interesting note about U-2 spyplanes and why it was
unlikely that a KWM-1 was ever installed in a U-2. I will ask his permission
to post his observations to the reflectors.
== 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>
Sent: Saturday, May 21, 2011 6:03 PM
Subject: Re: KWM-1 neutralization procedure
>
>
> On 5/21/2011 4:36 PM, AI2Q wrote:
>> I will study the schematics, Jerry.
>
> These neutralization circuits work with ratios of capacitors and were
> changed significantly when the 6146B came along replacing the ceramic
> variable with an air variable.
>>
>> What is the RCA phono jack for on top of the chassis on the KWM-1?
>
> Check to see if its connected like the transverter jack in a 32S-1 or -3.
> That with the PA screen disconnect switch would be for use with the 62S-1
> transverter.
>>
>> Also, does anyone have a schematic for the late model KWM-1s, like mine?
>
> The schematic I have is dated 1957, manual edition 2 from WA9VRH. The
> manual doesn't show that jack or that screen switch.
>
> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association
>>
>> == Alex
>>
>>
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