[Collins] KWM 2 issue

[Dr. Gerald N. Johnson]

On 1/31/2017 6:47 PM, Larry Shumway wrote:
> This issue started recently.
>
> When I power up my KWM 2 the meter pegs and stays pegged.
>
> Nothing happens and the meter stays pegged until I power it down.

Sounds like the RF gain control is full off either by being turned full 
counter clockwise or there is a wiring problem putting lots of negative 
voltage on the AGC line. I'd start with the power supply and make sure 
the bias supply filter capacitors are good and that the selenium 
rectifier has been replaced with a good silicon diode like a 1N4004 or 
1N4007. The selenium rectifier went bad 30 years ago.

The S-meter uses an IF tube as a vacuum tube volt meter to indicate AGC 
voltage which is generally zero at maximum gain. The voltage can go 
positive from grid emission but that pegs the meter below the zero 
setting. RF gain is reduced by applying a variable negative voltage to 
the AGC line.

Low screen voltage could also be a problem but I think its a way 
negative AGC voltage. Trace the voltages with a vacuum tube voltmeter.
>
> As it powers down the I can hear the receiver for just a second.
>
> Any ideas where I should start.
>
>
>
> Thanks in advance
>
> 73
>
> Larry, N5DHY
>
73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.
>
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