[R-390] R390/Solid State

[Barry Hauser]

Jim wrote:
> It is hard to believe, but this reflector is a gold mine of information on
> the R-390 receivers.  Unfortunately, as of late, the simplest question
seems
> to elicit hundreds of sophomoric responses.

Gotta disagree.  "Senior moments" yes, "sophomoric" no -- we're too old.
<sob>

> The R-390's follow the standard Collins receiver electrical design.  The
big
> difference is the ingenious mechanical tracking.

Yes, but that's not the half of it.  To most of us, the R-390's represent
more than just a clever clockwork.  They represent the pinnacle of mid-20th
century technology, a combination of mechanics, the very tops of the hollow
state, permeablility-tuned and "modular serviceability" arts.  A key
objective was to develop a true digital readout before it was really
practical -- as evident by, yes, all those gears and cams, but also the PTO
AND the coils.  Officially, there's only maybe one "solid state" item as
original equipment, but it's virtually guaranteed to fail, smoke and stink
eventually, so it doesn't count. ;-)

> Tube to SS conversions have not been too successful, but that is no reason
> for not trying.

Well, there ya' go.  It's like the mountain climber who climbs the mountain
because "it's there".  However, when a climber says he plans to go up the
wrong side of the wrong mountain, from whence no man has returned, we
brethren are duty-bound to dissuade him every which way we can.  Think of it
as a public service.  Awright, there's also the matter of tradition, which
can be dangerous to mess with, provoking unrest amongst the masses.

Judging by the rapier wit of Mike's reply, I'd say we did our duty.  He may
well proceed with his quest, but better conditioned and toughened up for the
task.

In fairness, there may be some good basis for such a project.  While most of
the tubes are still available at reasonable prices, there has been some
indication that time is taking its toll with leakage, etc. and a lot of
these tubes have been shipped around repeatedly increasing the possibilty of
internal damage to filaments and shorted elements on NOS supplies.  So, it
might be a good idea to cover the bases.  If it becomes impractical
(expensive) or impossible to keep these going 100% hollow state, truth be
known, most of us would revert to solid state at least on a stage-by-stage
basis to keep them running.

However, I would strongly recommend, Mike:  Keep your R-390 intact as a
working reference.  Pick up a junker, and/or some spare working or
non-working (cheap) modules, and work with those.  While Fair Radio doesn't
have any more non-A's, they do have parts not listed in the catalog and
others have odd parts and modules they could supply.

For some modules, it makes more sense to start from scratch with a clean Bud
chassis arranged to drop in -- such as the audio/VR module.  A solid state
version can be much smaller, leaving room for new "enhancement" modules --
product detectors, synch detectors, and even (forgive me Great Engineer in
the Sky) DSP.  The remnants of the audio module would just get in the way --
that part wasn't anything special performance-wise and sandbags the audio
response.  What others?  Maybe just the xtal calibrator, but it's fairly
small to start with.  Maybe the PTO, if you can whip up a synthesizer yet
keep the noise out.

Another approach is the one-for-one "solidtube" thing.  I suspect that's a
tall order and if possible, might run as much as $20-30 per unit, if
possible.  Not particularly attractive until the tubes approach that price,
but who knows?

>Good luck with your project and please keep the community informed on your
progress.

Amen on that one -- just as long as you don't wreck any good '390's in the
process or we'll sic a bunch of sophomores on ya'.  <WHACK! SMACK!>  No, no
... It's your radio, do what you want with it.  I'm a bit conflicted on this
issue, and now I'm bleedin', so gotta go.

Barry