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

[Brett Gazdzinski]

Great news.
Fun playing with the old stuff, no?

What I did with the one I had (the one I got for free but had to rent the 
guys hand truck for $10.00) was to solid state the rectifiers and in the 
sockets installed two of the bigger VR tubes for the modulator screen 
regulation, through a dropping resistor from the high voltage, not a center 
tap off the filter capacitors.
I always thought that unbalanced the caps and would have more voltage on 
one....

That DX100 was my learning radio, I tried every crazy experiment I heard of, 
new audio circuits, 600 ohm microphones, line level input, 6146 modulators, 
then kt88's, different mod transformers, outboard modulator using 811's, all 
sorts of crazy stuff.

I learned  LOT on that rig.

Brett
N2DTS



----- Original Message ----- 
From: "Rick Poole" <wa1rkt at arrl.net>
To: <amradio at mailman.qth.net>
Sent: Saturday, December 17, 2011 7:50 PM
Subject: [AMRadio] Possible success? (was DX-100B on Phone - bad audio 
distortion /oscillation)


>
> 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
> neutralization??
>
> 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!  :-(
>
> Rick WA1RKT
>
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