[Boatanchors] Hammarlund Super Pro 150 question

[Richard Knoppow]

    I had a look at the later versions. No values given in any of 
them for any resistor. In the military versions the value of the 
sensitivity pot is 50K, the voltage across it is approximately 
-22 volts. I was hoping I could find a tube pin where a 
comparative value could be found but connections are too 
indirect. I wonder if there is a Rider or other after market 
instruction sheet with values on it. Since the circuit is 
virtually identical with the later version my guess is that the 
value is the same. This brings to mind an interesting question; 
are RF gain controls usually linear or log? I never thought to 
check. The only one I have had to replace recently was on my RCA 
AR-88 and I was able to get an original part. I suspect they are 
log or audio taper pots. I have a BC-779 and am quite familiar 
with its insides but that is no help with this.
    FWIW I consider the Super Pro to be a very fine receiver, its 
main fault is drift, they really must be allowed to run 
continuously to be stable. Also, I found on mine there is a 
considerable amount of pulling of the LO from the AVC. Installing 
a VR tube on the LO cures that. Hammarlund did this with the 
HQ-120-X, I wonder why they never did it for the Super-Pro.

On 4/13/2021 10:49 AM, Al Klase wrote:
> Gang,
>
> In light of the ensuing discussion, I took a look at my 
> SP-110X. Unfortunately, it's not easy to get to the sensitivity 
> pot.  So I made some measurements from the 3rd IF grid cap to 
> ground with the switch in the "manual" position.
>
> Sensitivity setting:
>
> 0    106K
> 1    174K
> 2    176K
> 3    176.5k
> 4    138K
> 5    124k
> 6    117K
> 7    114K
> 8    113k
> 9    111k
> 10   110k
>
> So my SWAG (Silly Wild-Assed Guess) is that the sensitivity pot 
> is about 150K with an /_antilog taper._/
>
> Circuit hot shots, please check this out.
>
>
> 50-100K linear would not be disaster.
>
> 73,
> Al
>
> On 4/12/2021 11:36 PM, Al Klase wrote:
>> Wally,
>>
>> FWIW, the sensitivity control in the SP-200 is 50K per the 
>> manual.
>>
>> Al
>>
>> On 4/12/2021 7:06 PM, Wally Gibbons wrote:
>>>   Greetings,
>>> I'm overhauling a SP150 I got a few years ago. The 
>>> sensitivity control is
>>> bad. The resistor element is missing pieces. Therefore I 
>>> can't measure the
>>> end to end resistance of the original for a correct value.
>>>
>>> The schematic of the SP150 is apparently identical to the 
>>> SP110 minus the
>>> crystal filter. But the sensitivity control resistance is not 
>>> called out in
>>> the service data.
>>>
>>> Does anyone know the value for the sensitivity control?
>>>
>>> Thanks..
>>>
>>> Wally Gibbons, AF7FH
>>> North Logan, Utah
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>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL