[Collins] KWM-1 neutralization procedure

[Dr. Gerald N. Johnson]

Its labeled converter output in the 32S-1 and that is where the drive is 
tapped for the 62S-1 through a 1 pf coupling capacitor off a 6146 
control grid with a 47 ohm resistor to ground.

I don't have a 62S-1 manual but I suspect there's a paragraph in there 
about using the KWM-1 by adding the screen switch and that RCA connector 
or maybe it was in the later runs of the rigs that the handy KWM-1 
manual I have doesn't cover.

On 5/21/2011 5:56 PM, AI2Q wrote:
> 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.

The air variable didn't come in until the 6146B needed to be neutralized 
which the circuit with the ceramic variable couldn't do. And the ceramic 
couldn't take the heat of the extra RF current of the slightly larger 6146B.
>
> 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.

The use of RF feedback and worrying about the linearity by tube choice 
made a rig with less distortion than any solid state and most of the 
competition's tube rigs using sweep tubes. Collins set very high 
standards for distortion and was not satisfied with 3rd order poorer 
than 30 dB down and higher order products noticeable at all. W0WL has 
told me he worked on the KWM-1 PA for half a year or longer getting it 
clean, and at one point had a phone conference with RCA convincing them 
to build a more linear 6146(which became the A) he said. He was given 
that task because he had tamed a 6146 or two in his home made HF mobile 
that he use while driving to work at Collins and was heard by Art with a 
fairly clean signal. So its intentional that it sounds good. Just tickle 
the ALC and it will stay clean. Over the years, W0WL has built much of 
his own ham gear and it looks like factory, though one of a kind. He is 
careful with his work.
>
> 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.

Takes lots of voltage and that's probably a swinging choke so the 
inductance varies with DC current to some extent. The schematic of the 
516F-2 KWM-2 and 32S supply is practically identical, just uses three 
30s in series instead of the single 10 in the 516F-1. Be sure to replace 
the selenium bias rectifier before it fries the bias filter capacitors 
and the radio. The best replacement is a three terminal terminal strip 
(solder type) and a 1N4004 or 4007.
>
> 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.

I recall seeing a U-2 at the SAC museum with a KWM-1 mounted behind the 
pilot's seat. That's said to be why the crystal control module (also 
sold for novices) was created. Its entirely possible different commands 
used different radios. Its a little hard to believe a domestic radio 
made for sea level operation could operate in an unpressurized aircraft 
at 80,000 feet without arcing everywhere there was B+.
>
> == Vy 73, AI2Q, Alex
>
I can't post to the kwm-1 yahoo group so I cut that from the addresses.

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