[Collins] Ailing KWM-2

[Jim M.]

This has sometimes happened to mine because of corrosion or poor
electrical contact between the little cans that cover the exciter coils
and bandswitches.  They are supposed to provide sheilding that prevents
feedback.  If this shielding degrades, feedback occurs and the rig may
oscillate "out of band", hence the strange dip frequency.  You can
loosen the nuts holding the cans from the top and move them around to
break down the corrosion, see if that helps.  Be sure to retighten the
nuts but not too tightly. 

Donna & Robert Littleton wrote:
> 
> I am continuing to try to diagnose a problem in the transmitter stages
> of a 1963 vintage WE KWM-2.  The transceiver suddenly developed
> problems about two weeks ago.  I have gotten the receiver section back
> in operation, but the problems in the transmitter stages continue to
> elude my detection.  Here are the symptoms:
> 
> I get a larger than normal dip in the the plate current when tuning the
> PA.  The current dips way down to about 70 mils.  Also, the dip occurs
> off frequency from its normal location.  For example, when the radio is
> set for 20 meters, the dip occurs when the tuning knob indicator is
> within the 21 mhz markings.  The same is true on all other bands - the
> pointer is in a higher frequency range than it should be at the point
> of dip.  In addition, there is absolutley zero power output;  however,
> my frequency counter senses RF around the PA cage at the correct
> frequency (14.2 mhz in the particular case checked).
> 
> Here is what appears to be working okay:
> 
> The finals and driver - changed with no effect.
> TR relay (K3)- Continuity checks (with no power, of course) indicate
> that it is functioning correctly.
> I see no obviously smoked or overheating components.
> The band switch cord to the PA compartment and the switch itself within
> the compartment are working as they should.
> I have checked the resistance and voltage values of the pins of each
> tube in the transmitter chain, and all are either right on the money,
> or very close to specified values.
> The plate voltage blocking capacitor.  I do not have a capacitance
> tester, but the capacitor is not shorted and is leaking DC to its
> output side.  I assume that if it were open, I would get no dip at all
> in the plate current.
> 
> Can anyone help me diagnose this problem?  I'm about out of guesses.
> 
> 73,
> 
> Bob, KB4X
> 
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