[R-390] R390/Solid State

[email protected] [email protected]
Fri, 9 Aug 2002 18:27:17 EDT


Hi Mike- I've been reading the mail, but in the interest of bringing up your 
ratio of serious replies- I'll offer a few opinions:  I'm also an EE (not yet 
retired). 
I converted an old Super Pro to solid state back in the 70s.  In that case, 
the objective was to reduce the drift.  It did OK, but no other improvement 
that I can recall over the original radio.  I eventually gave  it away, and 
it was likely scrapped.  As others have noted, this conversions used 
dual-gate FETS, which are harder to find than tubes.
I've had a low-mileage R-390A for about 25 years, but the thought has crossed 
my mind about improvements.  Tube life has not been an area to improve, I 
don't think I've replaced more than 4 tubes in 25 years (and I've got enought 
spares for another 50 years).  So no good reason to change there.
I thought about improving the frequency readout- it sure is impressive to set 
my new solid-state receiver to the nearest 10 Hz.  I concluded, however, that 
300Hz is good enough for any use I would have, tho I'm still thinking about 
how to set each band so that you don't have to calibrate each time.  So no 
strong reason there, tho it might be nice.  As one of the other posters 
noted, you can buy or make an external readout for the PTO.  Still needs to 
be set to each band.
In terms of sensitivity and strong signal performance, the R-390 can only be 
equalled by a few commercial solid-state receivers (if you've got $20K for 
one).  so probably a minus for any solid state substitution.
Same for drift- almost negligible despite the temperature rise because of the 
tube heat.  Not as good as newer solid-state, but no great need for 
improvement with drift of a few hundred Hz.
Finally, the greatest weakness is the lack of SSB detector.  Thid really 
needs improvement!  I compromised on this one- I built a solid state product 
detector and AVC that connects to the radio's IF output, and audio and AVC 
terminals on the back of the radio.  This allow seamless operation of the 
radio in SSB, using all of the front panel controls.  Just a little box on 
top of the radio.  And no holes in the radio, which I assume will fund my 
grandchildren's college education someday.
The one drawback to the product detector is that I need to manually offset 
the BFO for sideband selection, thus I need to recalibrate when switching 
sidebands.  I'm now working on a new version with some surplus 100 KHz 
filters, which will allow sideband selection without recalibrating.
Once I get that done, I think it will be close enough to perfect for my 
purposes. 

However, if you launch into some work- keep in touch.  I'm still looking for 
the solution to get the crystal oscillators exactly on frequency.