"Henry Kolesnik" wrote in
message ...
I ended up with this & it's separate power supply in a
package deal, couldn't buy what I wanted without taking it.
It looks better than average but doesn't have the original
S-meter. Both are rack mount units in cases with a heavy
interconnecting cable, and they are heavy! It covers 1.25
to 40 Mc in 5 bands. Both units have aluminum tags with
serial numbers and the Rx is stamped Type O with a 40,000
serial. I've heard that they have terrific audio but with
only a portion of BCB it's a bummer.
I'd like to know a bit more about it and if they have any
value as collectors items or are they true boat anchors?
Is it a BC-794 A or B or a SP-210-SX or what? Why did
they make the power supply so heavy?
Thanks

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73
Hank WD5JFR


There were three versions of the SP-200/210 made and
offered as both civilian and military receivers. The
difference was mostly in the frequency range covered. The
ranges we
540 Khz to 20 Mhz, 1250 Mhz to 40 Mhz, and an LF version
where two of the bands covered 100 Khz to 200 Khz and 200 to
400 Khz plus 2.5 Mhz to 20 Mhz. The 100 to 400 Khz bands
were used for aircraft communication. This LF model is the
BC-779, the other ranges had other military designations
(which have now escaped me).

The standard model has resistors in the RF sections of
the broadcast band to broaden out the bandwidth and allow
for high fidelity reception. I think the BC-779 may have
also have these in the two LF bands. The 1250 Khz to 40 Mhz
model has shunt-fed RF sections rather than series fed to
narrow their bandwidth and improve image rejection
especially on the highest band. Other than these variations
in the RF sections the receivers are identical.

You may have the 25hz version of the power supply, it
has a huge power tranformer and is very heavy. It was
intended to work also on 50/60Hz power. Many parts of the
world had 25Hz power when these receivers were made (and
some still do).

These guys are not collector's items and were made by
the thousands. The version you have is the most desirable
one as a ham receiver. I think you are not missing much by
not having the broadcast band, most AM stations now use so
much processing that a wide band receiver will sound very
unpleasant.

I used a BC-779 (with 25 hz supply, ugh) as my station
receiver many years ago. I tried all sorts of modifications
to the RF stages but wound up restoring the original
circuits. They are bulletproof and the relatively high
receiver noise is of no concequence on the HF bands,
especially in the big city. The RX is, however, vulnerable
to voltage drift. I installed a voltage regulator for the HF
oscillator, otherwise the thing will change frequency as the
RF gain changes. With regulation its quite stable.
There is no temperature compensation in the Super-Pro
so for good stability it should be run continuously. When
that is done, and with voltage regulation, it is
surprizingly stable. Because the RX has three IF's and an
isolated and amplified AVC the skirt selectivity is quite
good and its possible to increase BFO injection without
upsetting the AVC. They are actually pretty good sideband
receivers.
Don't know if original meters are available. The
original is illuminated by a screw base lamp projecting into
the meter.
When these were made they were the best receivers
obtainable. One military handbook I have in storage
somewhere shows comparison charts of spurious responses for
several common military receivers c.1945. The Super Pro is
very clean showing essentially only one image response. In
comparison the SX-28 graph looks like a cornfield.
I have not worked on mine for a very long time but
probaby remember some hints and kinks if you ask. Actually,
I want to dig it out and put it back in service.
Another note: most of the military Super-Pros were rack
mount versions with a shrowd type covering. This is probably
good for shielding but has no ventillation so the chassis
gets very hot. I drilled perforations in mine, maybe a
mistake, but that was more than 40 years ago.
I eventually found a couple of table type rack cabinets
for the RX and PS. Because the PS is separate, unlike the
SP-600, both will fit into any standard table cabinet.
There are several downloadable manuals for all versions
on the web. BAMA is a good place to start but there are
higher res versions available elswhere.


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--
Richard Knoppow
Los Angeles
WB6KBL