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

[Bob Camp]

On Aug 31, 2014, at 3:44 PM, Charles Steinmetz <csteinmetz at yandex.com> wrote:

> 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.

or just get an amplified speaker.
> 
>> 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.

The output impedance of the tubes is the issue. It’s actually quite hard to find devices that will drive the tank coils in the radio without loading them down. Been down that road.

> 
>> 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.

I guess we do not agree on the meaning of quotes around a term to indicate a non-standard usage ….

Bob

> 
> Best regards,
> 
> Charles
> 
> 
> 
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