[Collins] KWS-1 RX mute issues.

Tue Jun 3 23:48:01 EDT 2014

Mylar whatever it comes from is great stuff. But not all paper 
protectors use mylar and your original post didn't specify mylar paper 
protectors. There is a huge difference in survival.

In many receivers the mute is relatively low voltage, IF stage cathodes 
if that's the RF gain control, or a negative DC bias on the AVC/RF gain 
control line. Putting a 350 volt B+ on the exposed contacts of the 
antenna relay would not be safe.

Had your specification for the page protector included "Mylar" I would 
not have commented.

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

On 6/3/2014 7:25 PM, Bill Riches wrote:
> I have repaired relays in the past using the mylar from paper protectors,
> the oldest being in a KWM-2 that has been in daily use for about 10 years
> after the repair with no problems, yet.  In the 7 or so KWS-1 transmitters
> that I have restored, five of them had stock antenna relays but not enough
> external contacts to use for receiver muting.  If you were to use an antenna
> relay with extra contacts you must disconnect the hot keyed rx line that has
> 350 volts on it and put heat shrink on the removed wire.  You don't want
> someone else to play with the mute line and get zapped.  You could die.
>
> Sorry to be so windy with my comments and findings but us folk that have
> worked on our ancient gear have to remember that the newbies of our group
> appreciate more detailed info as we all did when we were just learning.
>
> This should end this thread!
>
> 73,
>
> Bill, WA2DVU (Technical advisor and janitor for dB Electronics!)
> Cape May, NJ
>
> Subject: Re: [Collins] KWS-1 RX mute issues.
>
> A workable solution, though the plastic of the paper protector probably will
> wear through. A bit of mylar like from a drafting original would wear
> better. Or thin fiberglass circuit board. Another work around might work if
> the antenna relay has auxiliary contacts, they can do the receiver muting.
>
> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.
>
> On 6/1/2014 7:07 AM, Bill Riches wrote:
>>
>>
>> Noticed that my KWS-1/75a4 rig was not muting at times. Found a
>> problem in
>> K101 and here is how I fixed it.
>>
>>
>>
>> Pin 9 of K101 has 350 V that contacts pin 8 when keyed.  Pin 8 of
>> relay moves pin 6 of relay to open rx mute circuit.  There is a black
>> insulator at moves pin 6 from pin 8.  This insulator breaks down and
>> puts the hv on the mute line.  Good news! You do not have to replace
> relay.
>>
>>
>>
>> I cut a 1/8 x 1 inch of plastic sheet from a page protector sheet and
>> put it between the insulator and the actuating relay leaf.  A drop of
>> GC service cement at the base of the leaf seems to hold it in place.
>>
>>
>>
>> Working on the rig with the right side down on the bench puts
>> everything in sight.  At least these contacts were accessable.
>>
>>
>>
>> To check your rig: Disconnect mute lines from rx,  check for voltage
>> between both mute lines from tx with tx keyed (hv on), and if you see
>> ANY voltage you have a problem.
>>
>>
>>
>> 73,
>>
>>
>>
>> Bill, WA2DVU
>>
>> Cape May
>>
>>
>>
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