>> MY opinion is the following:
>> 1) replace one or both of the IF filters, if both are
>> done, a variable cap must be added across X2 and a
>> switch must be added to go between the filters.
>> 2) remove the purple wire and stop the tuning pops
>> 3) add two caps for the Xtalk fix
>> 4) add a cap to increase bass response
>> 5) add a cap to further reduce AC hum
>> I would not do the hiss mod and I would either replace
>> the speaker or use a nice external one.
>> a lot of the other mods are a waste of time. I won't
>> mention which they are but I have tried most of them.
>> I think I recently made the worlds best DX-394 by doing
>> all of these mods. I used a Hi-Fi filter in the wide
>> position, spec is 8/12. and a DX filter in the narrow
>> position, spec is 5/7. I can handle anything now
> What about the strong signal overloading (intermod's)
> that others have mentioned?
That's a problem with every radio at some level, moreso with very sensitive
ones with wide tuning ranges and lower cost - that description fits the
DX-394. To the best of my knowledge, nobody has succeeded in making a marked
improvement to overload with internal mods. I experimented with increased
bias on the internal RF preselector switching diodes and obtained subtle
improvement. I have been wanting to replace them with PIN diodes but have
yet to source some suitable surface mount devices. However, I suspect the
main intermod generator is the RF amplifier or the 1st mixer.
Fortunately, huge improvement can be made by external pre-filtering; and
this is true for any receiver with an antenna input jack that suffers from
Mike, you are rightfully proud of your modified DX-394's but to assert it's
the "world's best DX-394" is an exaggeration. There are others who have
installed superior filters (narrower Collins mechanical, e.g. 2.3/4 to use
your notation) and have made the necessary changes so that the upper and
lower BFO frequencies and filter are properly aligned for true single
sideband, not the compromise you have made by placing the BFO in the middle
of the passband. That makes their modified DX-394 better than yours for
SSB/CW reception. And if that sharper filter is switchable for AM mode (a
trivial mod compared to replacing the filter), then it's better than yours
for picking out one sideband or the other in a crowded SWBC band where the
channel spacing is 5kHz.
To disparage other mods as a 'waste of time' is provocative. That reflects,
in part, your interests and values and perhaps your marketing objectives.
Elsewhere you have stated that you are not interested in SSB/CW and digital
modes - some of the other mods are of primary benefit to these modes. And to
make the claim of a "hi-fi" filter (the stock AM filter that is widely
denigrated for being too wide could be so described, too) and place so much
emphasis on audio improvements (bass and hum) without also recognising the
benefits to the quality of amplitude modulation reception of certain AGC
mods and the ANL Defeat mod seems to be inconsistent with achieving the
"best", even for AM.
"Best" for one person is not necessarily "best" for another. Cost ($ and
effort), location relative to powerful transmitters, bands/modes of
interest, etc. will all factor into each person's evaluation of a receiver
and the possible improvements that can be made.