[Collins] Re KWM2A V13

[Dr. Gerald N. Johnson]

The two 68K 2 watt resistors are in parallel and set the cathode bias
and so the threshold of the vox relay tube. A 33k 5 watt wirewound or
metal film is a fine and permanent replacement.

I would think the open bypass on VFO socket pin three allowed some
transmit stage or stages to oscillate and either that stage was blocked 
not passing signal frequency or the oscillation was detected and caused 
a negative ALC voltage lowering the gain of the low level transmitter 
stages.

Those symptoms and cures are not what I'd find from ordinary circuit 
analysis. I am happy that you have found and reported them.

So the final inspector was human after all and allowed an unsoldered 
connection to slip through. The long term reliability of the unsolder 
connection isn't good, though with Collins rules insisting on a solid 
mechanical connection before soldering that can make a working radio 
with little solder until corrosion sets in from a humid environment or 
enough time in a benign environment. In that same era, Tektronix 
designed all their equipment with no mechanical connections, depending 
entirely on solder, in V slotted ceramic terminal strips (with the V 
slots metalized) so that a simple tug on each wire could test for proper 
soldering. If it moved it wasn't soldered.

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

On 2/15/2012 10:01 PM, Rick Gouge wrote:
> I`am reporting back to the list about my KWM2A findings. I replace
> the 2 , 2 watt 68k resistors in the bias circuit. That did not make
> any change but they were still abit closer to 33k then what was in
> there. I use  a big magnifying glass when i work and it sure helps my
> bad eyes to see again and they sure did. After a few hours looking
> and looking i found one wire from a cap to stand off that was not
> even soldered. I was so happy thinking i had found my problem. well
> the fix did seem to make the radio more stable but every now and then
> the alc would not zero on push to talk grounding, so i would have
> very low output. I hope this makes sence. If i pick the front of the
> radio up just a inch and let it drop everything would be good again.
> So back in i go and after about a half hour of looking i found it.
> The cap on pin3 of the  vfo power plug was broken. Big Smile. I
> readjusted my meter for alc zero, Perfect, i adjusted my meter for
> zero. Full power out and the alc reads perfec
>
> t on the meter at voice peaks. I would like to thank anybody on the
> list for the great info and your time. You would not believe how long
> i have been working on this gray box and how many times i put it back
> up on the shelf disgusted. Now i am smiling. 73 Rick VE7RiK
>