[GreenKeys] HAL ST-6

[keelan at beefchicken.com]

A quick update on my ST-6 adventure. I plugged my Model 28 in to the 
1/4" phone jack, and the 28 stopped bashing out nulls, so it clearly was 
seeing loop current. But as soon as I plugged it in, the space lamp 
stopped flashing on. I tried my other Model 28 (because I'm a slow 
learner), and got the same result. If you're less of a dope than I am, 
you might have figured the problem out already.

I spent some time scratching my head over the schematic, and poking at 
things with the meter. The loop current meter read 60mA, and obviously 
the selector magnet was staying operated. Back to the schematics, more 
head scratching.

Then I clued in. The ST-6 applied the loop current to the TIP of the 
plug, and keyed by opening and grounding the RING of the plug. The cable 
that I had on my M28 (the cable it came with) only had a TIP and SLEEVE. 
So, the TIP was feeding loop current to the selector magnet, while the 
ST-6 was happily removing and applying ground to the non-existent RING, 
which was directly connected to ground. The space lamp is directly 
connected to the SLEEVE as well, which is why it stopped working as soon 
as my teletype was plugged in.

With the correct plug installed, the TU works perfectly. My M28s on the 
other hand definitely need a cleaning and lube, and were not to happy 
with the cold in my garage. But overlooking the teletype failing to 
switch between FIGS and LTRS mode 50% of the time, the ST-6 is doing its 
job just fine!

- Keelan
VE7NCR