[Collins] KWM 2 issue

[Larry Shumway]

The RF gain is fully clockwise
It worked normally until this issue popped up so that eliminates wiring
issues.

thanks

-----Original Message-----
From: Collins [mailto:collins-bounces at mailman.qth.net] On Behalf Of Dr.
Gerald N. Johnson
Sent: Tuesday, January 31, 2017 8:24 PM
To: collins at mailman.qth.net
Subject: Re: [Collins] KWM 2 issue



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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