[Hallicrafters] SX-100 differences

[Tom NØJMY]

The info that Jim T. was able to mine from the archives is excellent! 
Now, I'd like to toss something out that I've been looking for for a 
long time:  What about differences between the Mk. 2, 2A, and 2B.  I 
keep running across folks that have 2B's that need re-capped.

Thanks in advance,
Tom

On 1/17/2010 3:11 PM, Jim Thayer wrote:
> Hi Jim&  the list,
> 	I found the following on my computer. For some reason yet to be determined - (hopefully soon),  the search function of the new archives on mailman.qth.net are finding only items in the month of January for whatever years since 2002.
> Jim
>
> Once you go Mac,
> You never go back!
>
>
>
>
> On Dec 5, 2005, at 5:14 PM, Jim Liles wrote:
>
> Re: [Hallicrafters] SX-100 MARK1A/MARK1B
>
>> Some of the differences between MARK1A and MARK1B are
>>    1)  The tuning capacitor has a slightly different drive like the MARK2
>>           I believe that the change was made to enable easy adjustment
>>           of backlash.
>>    2)  The 50 KHz IF is aligned at 50.75 instead of 50.50 KHz
>>           This is real magic for performance in combination with the slow AGC.
>>           It enables you to run the RF at full gain on CW and sideband.  It
>>           also produces better sideband separation and audio.
>>           Another reason for the change from 50.50KHz to 50.75 is the
>>           BFO bleeds backward through the IF transformer to the AGC causing
>>           the S-Meter to see a signal that is not there.  To test for this, simply
>>           set the BFO to 50.00KHz and switch from AM to CW/SSB.  You will
>>           see a significant increase in S-Meter reading.
>>    3)  The BFO is tapped off of the plate rather than the grid.
>>    4)  The AGC for sideband and CW is set for slow rather than fast.
>>
>> I have seen MARK1B's with some or all of the changes but all
>> had the tuning capacitor and 50.75 change which should and can be done
>> to all SX-100 models.  All the circuit changes to go from a MARK1A to a MARK2
>> can be done to any MARK1A with the addition of a two pole switch
>> for the AGC.
>>
>> This is probably not the right venue for long descriptions --- hope I have not
>> repeated well known info or bored anyone.  A merry Christmas and happy
>> holiday season to all.  ---  Regards Jim K9AXN
>
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