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