[Collins] 32S3 Transmitter self oscillation

[Glen Zook]

Check the neutralization capacitor.  If it is the earlier ceramic trimmer and if you are using 6146B/8298A or 6146W tubes then you need to stop transmitting immediately.  There is like at least a 95% chance that the neutralization capacitor will burn up.  You will have to go to 6146, 6146A/8298, or 6293 tubes.  If the neutralization capacitor is an air variable then any of the 6146 family of tubes should work fine.

In 1965 the military changed the 6146W from the 6146A/8298 to the 6146B/8298A with no change in the nomenclature.  This was because RCA originally said that the 6146B/8298A was completely compatible with the earlier versions of the tube.  Unfortunately, this was not true.  When the "new" 6146W tubes started to be used in the Collins 32S-1, 32S-2, 32S-3, 32S-3A, KWM-2, and KWM-2A it was discovered that the neutralization capacitors would "burn up" in a hurry.  Because of this Collins came out with a field modification kit which basically changed the neutralization capacitor to an air variable and changed several other components as well.  At that time all of the 32S-3, 32S-3A, and KWM-2 series in the manufacturing process were changed to the new neutralization circuit.

You also need to tighten EVERY machine screw and nut that go through the chassis.  All of the grounds in the transmitter are made through these and they definitely come loose and/or built up corrosion over the years.  This includes the machine screws that hold the tube sockets in place and the nuts that hold all of the shields in place.  A while back my 75S-3A started getting a little "squirrelly" and I tightened up all of these fasteners and the receiver started performing "like new" again.  In fact, even on newer units you have to occasionally tighten all of the fasteners since the grounds are made through these (including circuit boards).

Also, never mix a 6146B/8298A or 6146W tube with a 6146, 6146A/8298, or 6293 tube.  This is a recipe for disaster.  You can mix any of the earlier tubes or 6293 without problems.  But, again, NEVER mix the later tubes with one of the earlier versions.

Glen, K9STH

Website:  http://k9sth.com


--- On Sat, 10/11/08, Jaime Gomez <jgomez2005 at gmail.com> wrote:

From: Jaime Gomez <jgomez2005 at gmail.com>
Subject: [Collins] 32S3 Transmitter self oscillation

I have traced the problem in my 32S3 to a self oscillation, I am not sure if it is the drver or the finals which are self oscillating. Any one has had experience with it and can give me a hint what may be causing it?