"Henry Kolesnik" wrote in
message ...
Richard
The volume decreased with the filament transformer so I
need to open it up and see if someone made some mods. I
downloaded the military manual.
It seems to me that someone at Ham went nuts changing
model numbers for very insignificant reasons.

Note that the military type numbering was not done by
Hammarlund. The Super-Pro went through three versions, the
SP-100, the SP-200, the SP-400. The SP-100 was available in
three versions with different frequency ranges, the SP-400
in two ranges. The SP-100 was also available with or without
the crystal filter (I've never seen one without) but
evidently the filter could be retrofitted. All three were
also available in table or rack mount versions. There were
at least two power supplies, a standard and a 50 hz supply.
The 50hz supply will work on 60hz but not the other way. The
last military versions came with solid state power supplies.
There are some circuit differences between the
different frequency ranges. The standard version and the
aircraft frequency version (100 to 400khz) have series fed
RF stages with some loading on the low frequency range and
broadcast range of the standard version to broaden out the
RF bandwidth. The high frequency version (1250khz to 40Mhz)
has shunt-fed RF to keep the DC out of the RF coils. The
coils have ferrite cores so removing the DC sharpens them up
a bit, which is needed for a single conversion receiver
operating a the higher part of the frequency range. A
similar arrangement is used in the SP-400 and SP-400S (the
last has the same 1250 to 40Mhz range).
The three frequency range receivers had different
military type numbers.
The SP-210 is the same as the SP-200 but came with a 10"
loudpeaker, there was also a SP-220, again the same chaissis
with a 12" speaker. The standard version had an X on the end
of the number (SP-210X) indicating it had the crystal
filter, the high-frequency coverage version had an S on the
model number as well as the X for crystal, vis: SP-210SX.
The first versions, the SP-100 had glass multi-pin tubes
with external sheilds, the SP-200 was redesigned to use
metal octal tubes with do not need external shields.
Otherwise the circuits are pretty much the same.
The main virtue of the Super-Pro was the band switching
arrangement. This is a very complex system of knife edge
switches operated by cams, presumably to reduce lead length.
National achieved something similar with the plug-in coils
on the HRO and the sliding RF box on the NC-100, 101, and
later NC-200 and 240 types. This may actually be a better
arrangement. Hammarlund caught up by using a rotary turret
on the SP-600 and Pro-310. But, except for Hallicrafters
version of the Super-Pro, which also has a turret, I don't
know of many receivers that used this good, but complex
arrangement. One virtue of the Super-Pro is its excellent
interstage shielding and lack of spurious responses,
probably at least in part due to the RF stage arrangement.
It is also a relatively low radiation reciever.
Note that both the sliding coil method of adjusting the
mutual inductance of the IF stages (and hence bandwidth) and
the type of crystal filter circuit were Hammarlund
exclusives. The IF bandwidth arrangement allows symmetrical
expansion of the response curve where some other methods
cause the bandwidth to expand only on one side. The crystal
filter is arranged to vary the Q of the loading coil and,
again, does not change the center frequency or gain as the
bandwidth is changed, plus it uses a butterfly capacitor to
adjust the phasing again so the center frequency does not
vary with the notch position. This is a much more
satisfactory system than the original Lamb filter used on
National and Hallicrafters receivers until pretty late in
the game.
I have the civilian version of the instruction book and
will post it to you via private e-mail if you can't find it.
I am still on a dial-up and its pretty big but its yours if
you desire. BTW, it has a long list of the patents used
(mostly RCA and Hazeltine Labs) some of which are
interesting to chase down.



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Richard Knoppow
Los Angeles
WB6KBL