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

[wb3fau at att.net]

Or, maybe the antenna is the problem?  lets try  running  it  into a 
good  dummy load and see what  it  does...

--- On Sun, 12/4/11, ne1s at securespeed.us <ne1s at securespeed.us> wrote:

> From: ne1s at securespeed.us <ne1s at securespeed.us>
> Subject: Re: [AMRadio] DX-100B on Phone - bad audio distortion / oscillation
> To: "Discussion of AM Radio in the Amateur Service" <amradio at mailman.qth.net>
> Date: Sunday, December 4, 2011, 7:39 AM
> 
> >
> > 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.
> >
> 
> Perhaps a VHF parasitic, then? If it was a neutralization
> problem, the
> final would be oscillating fairly close to, but not exactly
> on, the
> frequency it's tuned to. Can you locate the frequency in a
> monitor
> receiver? Check out the parasitic suppressors - have they
> been modified or
> otherwise screwed up? Another thing that might help if it's
> a parasitic is
> "stopper resistors" on the 6146 grids - say, a 33 ohm or 47
> ohm resistor
> in series with each control grid, right at each 6146
> socket.
> 
> > 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.
> >
> 
> OK, that makes sense now. The modulator is out of the
> picture.
> 
> > 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 think you are on the right track.
> 
> > I'm just trying to figure out whether I should remove
> the
> > neutralization mod before installing the 6146A's.
> >
> 
> I wouldn't - I'd see if I could neutralize it after
> replacing the tubes,
> and only modify or remove the neutralization stuff if that
> wasn't
> possible.
> 
> 73/GL,
> -Larry/NE1S
> 
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