[AMRadio] Possible success? (was DX-100B on Phone - bad audio distortion /oscillation)

Rick Poole wa1rkt at arrl.net
Sat Dec 17 19:50:09 EST 2011

Well, things are looking up with the DX-100B.  The old girl does seem 
like she's settling down and doesn't seem so eager to fly off into 
the puckerbrush at the least provocation.

So far, at least.  :-\

Summary of the things I have done...

1.  Removed the modification to permit operation with the SB-10.  I 
can't imagine ever wanting to run this transmitter with a sideband 
adapter anyway.

2.  Restored the transmitter to its original circuitry in the RF 
section, as best I can tell.  There were many modifications in the 
audio section that I left in place.

3.  Replaced the 6146B 's with 6146A's and removed the neutralization 
wand, which didn't seem to be any help anyway.

4.  Replaced all caps in the PA section except the HV blocking and HV 
bypass caps (don't have any of those yet).

5.  Changed the power cord so that the hot side was fused instead of 
the neutral side :-/.  This didn't help the stability but it did help 
my longevity!  :-(

6.  Loosened and retightened all screws that were responsible for 
grounding anything, including one of the screws that holds the PA 
shield in place (couldn't get at the other one).

7.  Soldered the PA shield to the chassis in one place.  Plan to do 
it in more places if needed.

8.  Made up and installed some new parasitic suppressors to replace 
the old ones.

9.  After doing all of that, changing the plate tuning made a huge 
difference in the grid current (I'm told that indicates a need to 
neutralize), so I made up a new neutralization wand and installed it, 
and tweaked it back and forth so that now the difference in grid 
current is only just perceptible.  Who sez the DX-100 doesn't need 

I still need to replace the two 10K 10W resistors in the PA screen 
circuit with some 15-watt parts that should be in mid next week.  So 
for now I'm running the transmitter outside of its cabinet.  Good 
thing everybody in this neighborhood has cable TV!  :-)

Been running it occasionally on 3885 for a couple of days now and all 
seems OK.  Of course the proof is going to be after I put it back 
into its cabinet and kill myself wrestling it back up onto its 
shelf.  Then is when the gremlins are going to reappear!  :-(


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