Jon Teske wrote:
I used to manage operations for the military that used R-390s in vast
quantities. It was not uncommon to have over a hundred of them at a
facility and thousands in our overall inventory. For what they were
designed to do they did a great job. As is mentioned they did not have
a product detector. I once saw a prototype sideband adapter, but
before it was adopted in any number, we went to newer solid state
receivers (none in the ham price category... 10K each and up.]

There was a military sideband adaptor available using sheet-beam tubes,
although I forget the nomenclature. There also were a lot of civilian
models that will work as well.

There were a couple problems we had with R-390's. The main one was
maintenance. The tuning scheme was so complicated you practically had
to be a mechanical engineer to fix one. The gear trains to control the
permeability tuning are a wonder to behold. They were cumbersome to
tune and military intercept operators who used them all day long
complained of "R-390" wrist because it took so much arm torque to
change the megahertz dial. It was time consuming to get from one end
of the spectrum to a different end. Some guys, particularly HF search
operators got carpal tunnel from tuning them day in and day out. They
consumed a lot of energy, particularly if you had a bunch of them
operating at the same time. We usually had air handlers to cool the
rooms they were in. The only reason they didn't drift is because ours
were on all the time.

They are phenomenally stable by the standards of the day, and the short
term stability is actually better than some PLL receivers today.

The audio quality is pretty bad, though, and the mechanical filters
on the 390A that are a godsend for pulling signals out of the noise floor
also contribute to severe ear fatigue because of the enormous group
delay. I get a headache listening day in and day out.

Of course a ham restorer dealing with unit quantities doesn't have the
maintenance management problems we had because a ham trying to fix up
one or two can probably scrounge up the parts or cannibalize another
like units, but we had to look at the R-390 and almost any other piece
of gear the military used in terms of life cycle support, personnel
costs, training tails, depot stockpiling and a host of other issues.
It was a good receiver that just wasn't supportable anymore. The same
could be said for the SP-600 series which was actually obsolete when I
entered the profession 43 years ago, but that hasn't stopped dedicated
hams from making them work in unit quantities.

The good news is that Chuck Rippel's shop down in Chesapeake looks like
the Ft. Devens radio refit facility did thirty years back. He has racks
and racks of 390s in for repair, and he has all the special tooling and
jigs for module testing. So you still have the depot level support that
the military provided, it's just that Chuck is providing it now.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."