[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.