[ARC5] Novice receivers.

[Richard Knoppow]

    Well, the Super-Pro began as the SP-100 and definitely pre-dated the 
HQ-120 but there were several models of the Super-Pro. I think the 
SP-200 was about contemporary with the HQ-120 but the Hammarlund 
patented crystal filter was not available on the Super-Pro until after 
the HQ-120.  Again, there WAS a sort of crystal filter on the SP models 
ending with X but it was of a simple and less satisfactory design.  The 
first receivers with the Lamb patent filter were made by National, 
probably the HRO which was their premium model. While the Lamb filter 
had variable bandwidth its gain and center frequency varied with the 
bandwidth setting. Other makers, such as Hallicrafters, used the Lamb 
type filter although there were differences in detail. For another 
approach to the design look at the crystal filter in the RCA AR-88. This 
filter uses a stepped load inductor with varible capacitors at each tap 
to keep the resonant frequency uniform with bandwidth change.  The 
"phasing" cap is used to balance the bridge of which the crystal forms 
one arm, but, unlike both Lamb and Oram, the cap is not of the butterfly 
kind that keeps capacitance to ground the same, so, while it does 
produce a notch its not a uniform one or very deep. I think RCA was 
trying to avoid infringing the Oram and Lamb patents.  They did provide 
a notch control in the AR-77 and brought the phasing control out to the 
front panel in late AR-88 type receivers without any change in the 
design. I have no idea of how the AR-77 filter performs.  The receiver 
was evidently intended to compete with the HQ-120-X but doesn't have 
some of the latter's features, for instance the band-pass, three section 
IF amplifier.  It does have air variable trimming capacitors and a 
shadow mask on the main dial. A curious receiver, its headphone jack is 
under a hatch on the front corner.

On 11/16/2015 3:56 PM, Fernando - LU2DFM wrote:
> Thank you very much.  I was with the wrong notion that the SP-200 was
> elarlier than th HQ-120.
>
>
> On Mon, Nov 16, 2015 at 03:06:19PM -0800, Richard Knoppow wrote:
>>      Yes, if you look at the Super-Pro data sheets you will find that before
>> about 1940 a crystal filter was offered as an add on but the design was
>> quite different. It was to be blunt crude, probably a work around of the
>> original Lamb patent.
>>     I mis-spelled the name, it is Oram.  The patent can be found at:
>>
>> http://www.google.com/patents/US2222043
>>
>>      The application date is 1939, issued in 1940.  The HQ-120-X was the
>> first receiver to employ this circuit. It was also offered as the HQ-120 (no
>> X) without the filter but I think very few were sold so the filter became
>> standard.
>>
>>     James J. Lamb had several patents on crystal filters, for instance:
>>
>>
>> US 2156786 A
>> and
>> US 2054757 A   which I think was the original.
>>
>>      You may also want to look at:
>>
>> US 2101549 A
>>      Lamb's patent on the noise blanker.
>>
>> On 11/16/2015 1:32 PM, Fernando - LU2DFM wrote:
>>> On Mon, Nov 16, 2015 at 01:20:25PM -0800, Richard Knoppow wrote:
>>>
>>>> This same filter, invented by Donald Orem, the chief engineer of Hammarlund,
>>>> was introduced on the HQ-120-X and was eventually used in the Super-Pro. The
>>> I always though that it was the other way around, since my understanding
>>> is that the Super Pro predates the HQ-120 for some years.
>>>
>>> Can you expand on this?
>>>
>>> Many thanks.
>>>
>> -- 
>> Richard Knoppow
>> 1oldlens1 at ix.netcom.com
>> WB6KBL
>>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL