[Collins] Kwm-2 rx pop noise

[Dr. Gerald N. Johnson]

Sounds like the AGC has the older single time constant capacitor and 
maybe it has been enlarged. The later KWM-2 had a dual time constant for 
the AGC.

My oldest schematic shows a 3.3 meg resistor between the wiper of the RF 
gain control and the AGC line with a .05 uf capacitor in parallel with 
the resistor. R83 and C93.

In a later schematic there are two resistors between the RF gain control 
and the AGC line (revision 25 in that manual) R83 is 1.5 Meg and has C93 
0.47 uf in parallel with it and R180 680K with C265 0.01 uf in parallel.

The 9th edition 1-78 of the manual shows the history of that change 
without dating on page 7-8 and refers to part A of Service Bulletin 8. I 
do have it in my archive thumb drive and it goes into very much detail 
on the update and says it prevents clicks on strong noise or signals.

My 75S-3B came with the dual time constant and it worked well. I copied 
it to a modified Q-5er with converter that I used alongside the 75S-3B 
and it worked well there too. A big capacitor without the dual time 
constant would be slow to respond and slow to drop off the S-meter 
indication. And so would have the click as you described.

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

On 1/30/2017 6:32 PM, Bill Riches wrote:
> Lately I have noticed a pop or snap noise when a strong station transmits.
> It is heard on the start of the first spoken syllable.  It is not heard as
> talking continues.  10/9 sig – the s meter takes about ½ second to go to
> minimum.  On the next transmission – s meter goes back to 10/9 and again the
> pop or snap sound is there.  I imagine it is an AGC or PD problem.
>
>
>
> Any hints before I dive into the rig?
>
>
>
> 73,
>
>
>
> Bill, WA2DVU
>
> Cape May
>
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