[R-390] R-392 market prices and availability?

[Charles Steinmetz]

Bob wrote:

>Before heading down the 392 route (been there done that) consider a 
>couple of things:
>
>3) Audio output is at best anemic. Yes there are ways to get around 
>this. Often radios are hacked to do so. It's certainly something to 
>ask about on any radio you buy.

There was a military SS replacement module that (IMO) stinks.  Maybe 
not as bad as the tube audio, but still horrible, IMO (though there 
are some who like them).  Requires a small modification to the radio 
to add this module.

There are also at least two decent mods for the audio:  There is a 
MOSFET replacement circuit floating around, attributed to "S. 
Johnson," that looks as if it would be a very good solution.  And 
there is a super simple mod I developed to make the existing 26A7 
output stage sound much better and preserve the life of the 26A7, 
which I described in a list message on 2/9/14 (this mod does not 
extend the capabilities of the anemic audio stage, which puts out 
less than 1/4 watt into 600 ohms -- it simply makes it sound much 
better).  I can send you schematics of these if you get a 392 and 
would like them.  If you do the super simple mod and then use the 
output to drive an external amplifier (push-pull 6V6s would be 
superb), the audio should be quite good.

I'd look for an unmolested original radio and then make whatever 
changes you decide are best.

>6) Some radios got fully solid stated way back a long time ago. I 
>would avoid those radios, the MOSFETS used are pretty much all gone. 
>The chopping and splicing to get it done often made reversing the 
>process difficult. I never saw a solid state version that worked as 
>well as the tube version of the same radio.

I concur regarding SS conversions you may find in the wild.  In 
principle, however, it should be possible to do a SS conversion that 
improves performance all around, while getting rid of the current 
draw and power dissipation of the tube filaments.  I've never had a 
392 of my own, so I've never tried it, but it would be a very 
interesting project.

>7) The 392 is a "no filter" radio. In other words the selectivity 
>comes from a bunch of tuned IF stages rather than a packaged 
>mechanical / ceramic / crystal filter. That gives it a bit different 
>sound than a lot of more modern gear. It also does not provide quite 
>the razor sharp narrowband selectivity that some other radios do.

It's not correct to say the 390 is a "no filter" radio -- it has 5 
big LC IF filter cans nearly identical to those in the famed 
R390.  Actually, this is an advantage compared to a 390A for almost 
all listening, IMO.  The 390A uses mechanical filters with pronounced 
group delay and ringing at the passband edges, which is unpleasant 
and fatiguing to listen to.  Consequently, once the audio-section 
problems are fixed, a 392 sounds much better than a 390A (when both 
are used at a power level supported by the 392, or with an external 
amplifier).  It sounds much like a 390, in fact (no surprise).  Some 
of us have installed R390 IF strips into our R390As for just this 
improvement.  See Tom Marcotte's outstanding 5/18/11 post on this 
list detailing the procedure.

Best regards,

Charles