[Hammarlund] Hammarlund SP-600 History Item

[Richard Knoppow]

----- Original Message ----- 
From: "Todd, KA1KAQ" <ka1kaq at gmail.com>
To: "James A. (Andy) Moorer" <jamminpower at earthlink.net>
Cc: "Hammarlund List" <hammarlund at mailman.qth.net>
Sent: Sunday, September 07, 2014 5:37 PM
Subject: Re: [Hammarlund] Hammarlund SP-600 History Item


> On Sun, Sep 7, 2014 at 6:37 PM, James A. (Andy) Moorer <
> jamminpower at earthlink.net> wrote:
>
>> I don't know, but here's what I would guess:
>> Their competition was the RBB, the AR-88, and the SX-28. 
>> All
>> single-conversion. The SP-400 was quite a good seller to 
>> the military (as
>> the BC-779). I would not be surprised if there wasn't a 
>> big Signal Corps
>> contract that came up and they needed a competitive 
>> advantage. The SP-600
>> looked and behaved a lot like the BC-779, but it was (is)
>> double-conversion. It was probably the cheapest, easiest 
>> hack they could
>> come up with to make a double-conversion receiver to give 
>> them a
>> significant competitive advantage. The imaging in 
>> single-conversion
>> receivers had been a continual drumbeat for a couple of 
>> decades, made worse
>> by the development of transmitting tubes that could 
>> actually hit that high
>> range (above maybe 20 MHz).
>
>
> Aside from some similarity in layout, I don't find a lot 
> of resemblance
> between the -600 and -200 series which the military bought 
> in large numbers
> for WWII. The SP-600 was actually spec'd as the R-274 
> along with the
> Hallicrafters SX-73. Both are excellent receivers for 
> their original
> purpose. The fact that there were so many different 
> version upgrades and
> numerous other agencies bought the SP-600, combined with 
> the fact that they
> were around for so many years (commercial users like ITT 
> were still using
> them into the 80s) speaks volumes. Far from a quick hack, 
> they were a well
> built, purposeful design.
>
> As to why the gov't bought so many SP-200s and later 
> variants, it's simple:
> they were available, tried and tested. SP-200s had been in 
> commercial as
> well as civilian service for several years before WWII 
> broke out. More or
> less in need of a lot of comms gear fast, Uncle Sam 
> grabbed them up then
> worried about the contract specs for later purchases. 
> Other civilain sets
> like HROs, SX-28s among others were procured. AR-88s had 
> already been going
> to the Commonwealth countries, England was also quite fond 
> of the HRO and
> S-27 VHF set.
>
>
>> Now why they went to the turret assembly, rather than the 
>> switched
>> arrangement of the above-mention receivers I will never 
>> know.
>>
>
> Halli used the same approach. A look at the original 
> contract might reveal
> the answer.
>
> The fact that there are still so many SP-600s around says 
> a lot about its
> utility. While we may find shortcomings and nuisance 
> issues today, mainly
> with old components, they seem to have worked quite well 
> for others for
> many, many years.7> ~ Todd/KAQ

     The turret arrangement was done to minimize lead length 
of RF leads and keep them all similar for different bands.
     The SP-600 despite some physical resemblance to the 
Super-Pro is a completely new design.  The Super-Pro was a 
very high performance receiver, despite being a single 
conversion receiver its image rejection was quite good and 
it had very few spurs.  There is a military handbook on 
communication, which I do not have at the moment, that has 
charts showing comparative spurious responses of several 
receivers of WW-2 vintage. The Super-Pro is very clean 
having only one image response while the SX-28 looks like a 
corn field with images and beats all over.
     The military used four versions of the SP-200, the 
BC-1004 which was the standard civilian version covering the 
broadcast band up to 20 mhz, the BC-794 which was the 
military version of the SP-200X which dropped the broadcast 
band and went up to 40 mhz, the BC-779 which covered 100 to 
200khz and 200 to 400khz in place of the two lower normal 
bands and covered from 2.5 to 20 mhz. This was used mainly 
for aeronautical purposes. There was a forth version, the 
R-129/U which covered from 300khz to 10 mhz continuously in 
five bands. I've never seen one so I suppose they are pretty 
rare.  The Super-Pro was designed to have high quality 
broadcast reception with a 14watt push pull audio amplifier 
and wide band IF.  The two broadcast bands had loading 
resistors across the RF coils to broaden them out a bit. 
The BC-794 uses shunt fed RF stages in place of the series 
fed ones in the other versions to get the DC out of the 
coils and raise their Q somewhat to improve image rejection.
    The "hack" if there was one was the post-war SP-400. The 
standard version covered from 540 khz to 31 mhz in five 
bands since it dropped the 2:1 ratio used on the previous 
models.  There was another version, the SP-400X which 
covered the same range as the HF version of the SP-200, 
namely from 1250 khz to 40 mhz.  All the Super-Pros from the 
200 series have the patented Hammarlund crystal filter 
invented by David Orem, their chief engineer. This was 
debuted in the HQ-120-X and used in all subsequent 
Hammarlund receivers that had crystal filters including the 
SP-600.
    The Super Pro series up to the late 400 did not have any 
temperature compensation although Hammarlund knew how to do 
it and used it in the HQ-120-X. The HQ-120-X also had a 
voltage regulator tube something the Super Pro needs badly 
since the LO pulls with B+ variations from the RF/IF gain. 
The SP-600 appears to have addressed these issues.
    Note that the RCA AR-88 has extensive temperature 
compensation of the LO with separate compensation caps for 
each band.
    At the time they were made the Super-Pro was the most 
expensive generally available receiver on the market.  Since 
no AR-88s were sold on the open market there is no price 
known but its estimated that they cost about twice what a 
Super-Pro did.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com