[Collins] KWM-2 instabilities

[Glen Zook]

What is the neutralization capacitor?  Is it ceramic or air variable?  If ceramic, make sure that the final amplifier tubes are original 6146, 6146A / 8298, or 6293.  Do NOT use the 6146B / 8298A or 6146W tubes.  You can also use the Japanese 2001 but NOT the 2001A.

 Glen, K9STH
Website: http://k9sth.net

      From: Al Parker <anchor at ec.rr.com>
 To: Collins Radio Association <collins at mailman.qth.net> 
 Sent: Saturday, August 19, 2017 2:15 PM
 Subject: [Collins] KWM-2 instabilities
   
Hi folks,
    I bought a KWM-2 about 9 mo.s ago, have tried to conquer its problems 3 
or 4 times since, with no luck.
    I have gone thru neutralizing PA, driver & fdbk.  Have tightened 
screws, swapped tubes in xmt RF string, DeOxited bandswitch wafers with 
needle applicator, ckd voltages & resistances on V7 RF amp & V6 mixer, 
all OK, no change in problem.
    It appears to be working well on 20-80m, but on 15 & 10 it is very 
unstable.  Plate current won't dip, but will vary with mic gain, plate 
tuning & exciter tuning.  It goes high, and output is on the correct 
freq., but when tuning the final plates, it oscillates and freq. changes 
with tuning.  Sometimes even with mic gain full CCW it remains 
oscillating, once it's started.
    On 15m, watching the final output on a scope, it varies abruptly in 
amplitude and freq. when changing exc. tuning.
    My hair gets thinner every time I look at this thing, any constructive 
thoughts would be greatly appreciated.
    I try to remember that we do this for fun, right?