[Boatanchors] KWM2A

[Glen Zook via Boatanchors]

Try replacing V-2, a 6U8.  The pentode section is the tone oscillator (V-2B) and disappearing grid drive is often due to a weak V-2.  Replace with a 6U8 and not a 6EA8 which generally works better than a 6U8.  For some reason, in the Collins S-Line and KWM-2- series, the 6EA8 often does not work well as the tone oscillator whereas in any other application the 6EA8 works very well.
A steady tone is needed for grid drive in the KWM-2- series when in the tune or lock key position on the mode switch. Glen, K9STH

Website: http://k9sth.net
      From: Bill and Liz <magoo at isp.ca>
 To: boatanchors at mailman.qth.net 
 Sent: Monday, January 5, 2015 3:07 PM
 Subject: [Boatanchors] KWM2A
   
I’m playing with a KWM2-A which has intermittent drive problems.  After turn-on, it may or may not produce grid current and, if it does, after a few cycles the drive disappears “until next time”.  Drive is always available up to the grid of the driver tube-the intermittent condition is after that.  I can find no blown or damaged components.  The only clue is that when drive is available it starts with a decent reading and then declines fairly quickly to about 1/3 of the initial meter reading.  I have tested the driver tube ; screen and plate voltages are always the proper value.  It is possible that it is a relay problem (driver tube is biased off in receive and switched by K2) but I inspected the relay, cleaned the contacts with paper and NuTrol and even rapped the relay with a screwdriver when drive disappeared, all to no avail.