[GreenKeys] ST-6 board

[epvgk at limpoc.com]

Hi folks,

I recently picked up a HAL ST-6 TU on ebay just because i'd never used a
"real" one and wanted to see how its performance compares to both a computer
and the small XR2211-based one I made for greenkeys. 

As i feared it arrived mostly intact but with three of the toroids rolling 
around loose in the case, however repair was not too challenging. 

What is challenging is that I can't use it on 850 shift because it's missing
the input / bandpass filter / limiter board for 850, marked "#1". Or at least,
it has two discriminator boards, one for 850 and one for 170, but only one 
input board (marked 170), and an empty slot. 

Other than that, it's performance is really impressive and does a better
job than the XR2211 PLL-based design with weak and/or noisy signals. 

So anyway - anyone have a scrap ST-6 with such a board? I'd like to use 
this thing to participate in the weekly Clatternet RTTY net, and they run
850 shift. If it matters, this appears to be an early unit, Serial #138. 
Very nicely and neatly constructed. 

eric