[Hammarlund] Old Hammarlunds

[Richard Knoppow]

----- Original Message ----- 
From: "Todd, KA1KAQ" <ka1kaq at gmail.com>
To: "Carl" <km1h at jeremy.mv.com>
Cc: <Hammarlund at mailman.qth.net>
Sent: Tuesday, April 12, 2011 12:26 PM
Subject: Re: [Hammarlund] Old Hammarlunds


> On Tue, Apr 12, 2011 at 2:48 PM, Carl <km1h at jeremy.mv.com> 
> wrote:
>> When a SP-200 can compare with a 1937 NC-101X or a 1939 
>> NC-200 for drift
>> then I might get one again. They both also have great PP 
>> audio.
>
> Mine ran circles around the NC-101X I had for stability 
> and audio.
> Which is why the National went to 'JN at the Richmond 
> 'fest in '09 for
> what I paid for it. Neat receiver but it was just after 
> the move and
> things were closing in on me again. It even had the green 
> tuning eye.
>
>> Its a shame Hammarlund never offered a good sounding 
>> external speaker, at
>> least the ones in the console versions of the Comet and 
>> Super Pro did them
>> justice.
>
> They did. It was a big field coil Jensen (12-15 inch?). 
> Got one with
> my SP-100 a few years back. It shows up in some of their 
> later 1930s
> ads. It appears they went the PM route when they deleted 
> the FC
> connections from the power supply, and those speakers seem 
> to be the
> ones that show up regularly, in the black wrinkle 
> cabinets.
>
> I bet you'll like the 400 once you bring it online. It 
> makes a big
> difference when you have an example running up to spec vs. 
> a tired
> version needing a recap, alignment, and all the rest.
>
> ~ Todd/KAQ

    I used a BC-779 as my station receiver for some years. I 
used several experimental LO and RF circuits in it at one 
time or another. The main improvement to stability was 
adding a VR tube regulator to the oscillator. The receiver 
was run continuously and was very stable once it came to 
equilibrium, which took a couple of days. The original dust 
cover acted like an oven causing the interior to become very 
hot. I took it off. The overall stability did not change 
significantly but the temperature was much lower with it off 
so I left it that way. I ran it in a standard desk cabinet 
which had enough ventillation to keep the chassis fairly 
cool.
    The stability was good enough so that I could monitor 
SSB networks without retuning for many hours. The VR 
regulator prevented frequency change with RF gain change, 
which otherwise is very noticable.
    The extended range version of the RX, which trades the 
540khz to 1250khz range for 20 to 40 mhz uses a different RF 
circuit with the amplifiers shunt fed rather than series 
fed. This probably increases the effective Q of the RF 
stages and reduces image response somewhat.
    Somewhere I have a military communications manual c.WW-2 
which has charts showing performance characteristics of 
various receivers available to the signal corps at that 
time. The Super-Pro is head and shoulders better than any 
other in terms of lack of image or spurious responses and 
some other characterists. The SX-28 looks awful in 
comparison. These were probably the best receivers available 
at the time and were also the most expensive. I think its 
likely the RCA AR-88A would probably have bettered it in 
some ways but does not seem to have been used by the signal 
corps. I am not sure when the AR-88 design originated, it 
may have been too late.
     The Super-Pro also had Hammarlund's exclusive variable 
IF, done with a mechanical arrangement to change the mutual 
inductance so that the curves remained farily symmetrical 
and did not change center frequency, plus Hammarlund's 
patented crystal filter, the best of the bunch.

     Another note, someone asked bout the Pro-310, it was 
from all reports, a dog. I remember when they came out 
lusting after one but they had a lot of problems including a 
low frequency IF causing serious image problems on the lower 
bands where it was single conversion. It was also a 
mechanical nightmare. Not many were built before they were 
discontinued and I suspect H lost a lot of money on them. 
They look sexy but were not very good receivers.

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