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

[Rick Poole]

In a private email, someone mentioned that it sounded like a 
neutralization issue.

That was my first thought but I can not find anything in the manual 
that mentions neutralization... not in the PA section, and not in the 
modulator section (or anywhere else).  I don't recall seeing anything 
anywhere that mentions that a high-power audio circuit, like a plate 
modulator, needs neutralization.

If I need to check that, anybody know how?

There is a length of wire connected to the driver tuning capacitor 
and running through the grommet in the PA compartment shield, where 
it runs over to an area between one of the transformers and the PA 
tubes, where it just stops, doesn't connect to anything.  I was told 
that this is for PA neutralization.  That is probably OK since on CW 
the transmitter is rock stable, no tendency to self-oscillate at 
all.  In any case, I couldn't find anything in the manual that 
discusses that so it appears to be some kind of aftermarket modification.

Rick WA1RKT