[Drake] AC-4 voltage stability problem

[Dan W. Dooley]

I'm having an issue with my AC-4 supply in that the DC voltage is not
steady.  Ripple doesn't seem too bad (under 6 v P/P) on the HV line at full
power out of the transmitter.  The problem is, the level of DC fluctuates up
and down by at least one volt on the + 650 volt line even in non-transmit
mode.  And, perhaps a half volt on the +250 volt line.  A smaller amount on
the bias supply line.

I have replaced all of the electrolytics within the supply.  Twice.  Same
thing.  I've also insured that all ground points are securely tied to the
chassis and together at several points around the chassis.

The fluctuation is not steady (cyclical) and really looks like the effects
of a loose connection but none has been found.  Scope measurements on the
primary side of the supply and also on the "input" side of the rectifier
diodes show those voltages very steady.  That makes me wonder if a diode
could be the problem.  I've not replaced those yet.

The amount of voltage fluctuation doesn't sound like enough to be
significant but I believe that it is having some effects on proper operation
of the transmitter.  Any thoughts?  Ideas?

Dan W. Dooley  WB5TKA
 email: dandooley@pipeline.com
 http://www.dooleystreasurechest.com