[AMRadio] DX-100B on Phone - bad audio distortion / oscillation

[Rick Poole]

At 02:56 PM 12/3/2011, ne1s at securespeed.us wrote:

 >>>>>
>Does the RF output frequency change when it goes into oscillation, and you
>kill the RF drive?
<<<<<

The SWR goes off the scale, which is a dead giveaway that the 
transmitter is putting out RF on pretty much any frequency but the 
one it's supposed to.

 >>>>>
>  I'm thinking perhaps the finals are taking off on their
>own, since they appear to be generating RF with no drive from the 5763. If
>so, you may need to add neutralization. But I can't explain why this would
>happen in AM and not CW.
<<<<<

It's happening in CW now, too.  It happens reliably when I tune a 
little off-resonance on the high side, i.e. the Plate pointer points 
to a higher number, and the plate tuning capacitor is more 
meshed.  Maybe that's why I didn't notice it on CW before.

The PA has a neutralization modification whereby a wire is routed 
from the driver capacitor to somewhere near one of the PA tubes, then 
you move that wire back and forth to find the sweet spot for 
neutralization.  I have tried every position of that wire and nothing works.

I've ordered some 6146A's to replace the 6146B's installed now, since 
some report problems with the 6146B's, and I know that some Collins 
KWM-2's, including mine, don't play well with -B's.  We'll see what 
happens when those arrive.

I'm just trying to figure out whether I should remove the 
neutralization mod before installing the 6146A's.

Rick WA1RKT