Re: {Collins} KWM-2 idle current changes with tuning



Try balancing the carrier.
If it is out of balance the transmitter will transmit some carrier and could
possibly cause the 'idle' current to go up...
Part of the current you would see in this example is caused by the
transmitted carrier so when you change frequency the PA goes off resonance
and the current goes up.
This would seem to be the case because as you said...then you change the
plate tuning the current goes up. This is normal but not when the carrier is
properly balanced.
After you balance the carrier the bias current will have to be reset to
40ma.
Let us know what the fix is.


73

David Harmon
K6XYZ
Sperry, OK

-----Original Message-----
From: Collins [mailto:collins-bounces+k6xyz=sbcglobal.net@xxxxxxxxxxxxx] On
Behalf Of Michael Jay Jones via Collins
Sent: Thursday, May 28, 2015 9:10 AM
To: collins@xxxxxxxxxxxxx
Subject: {Collins} KWM-2 idle current changes with tuning

This is my first post to this knowledgeable group.  I have an interesting
problem and perhaps someone in this group has had this issue and would be
able to share a solution or point me in the right direction to investigate
the cause.
 
I can set the idle current (bias) to 40ma, no problem.  But when I tune the
PTO, change the exciter, or change the plate tuning, the bias current
changes!  It can swing to 70ma or more or down to 20ma depending on the
tuning!  Changing the PTO, Exciter, or PA tuning will all change the
indicated idle current. 

The radio is working fine otherwise and I continue to make contacts with a
modest dipole antenna 10 feet off the ground with good signal and audio
reports.

What I have been doing is to tune up first and then double check and reset
the bias if necessary to 40ma.
This behavior started recently as I recall this was not a problem.  I have
had a few mishaps that let the smoke out on several occasions the causes of
which I located and damage repaired.  But perhaps I missed something?  It
was suggested that the KWM-2 will do this if the PA tubes are not
neutralized properly.  But I have changed the finals and checked the PA
neutralization many times now and I believe the issue is elsewhere. 

In the meantime I will continue to investigate but perhaps someone has seen
this issue before and can save me a great deal of time.  

I have checked the reflector archives.  There is one mention of a similar
situation but no solutions or explanation posted.  

I do have an electronics background and a fair amount of test equipment so a
technical discussion is welcome.

Thank you for the support.  

Regards,

Mike

KD9CNV
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