[Hallicrafters] SX-100 differences

[Jim Thayer]

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