[GreenKeys] ST6 questions

[Eugene Hertz]

Hello all,

I've been using an ST6 from ebay for several years now.  It has always done good service but the motor control anti-space circuit never worked which was ok by me.  I never had a chance to really look into it in any detail.

Recently I acquired 3 more ST6s on ebay and now have been able to do some comparative anatomy between them all. Very interesting findings. One has obviously been built from a kit, 2 seem to be factory and the fourth is unknown.

So I took the best of the 3 new ones and began comparing to my regular ST6 and I started looking at the frequency response. Here's what I got using my R&S Polarad SPN audio generator. ST6 #1 is one of the new ones, ST6#2 is my regular use TU.  Note that my regular unit does not have 425 shift.

ST6 #1	(new one)
MARK    SPACE   SHFT	
2150	2330	180
2150	2580	430
2150	3010	860

ST6 #2	(regular use)
2160	2325	165
2140	2975	835

So, how important is it to have the frequencies right? Or is it more important to have the total shift right. In the case of the shift for ST6 #1, they are pretty good varying 5-10 hz from expected. #2 is 5-15hz off a little worse.

Should I try to get the shifts more accurate to 5hz each?

My receivers only have BFO, no product detectors (YET) so I seem to always be able to tune the receiver or BFO to produce the right tones. However, I hope soon to own a product detector (outboard). How will this affect the need to have the tones accurate vs the shift?

Second batch of questions.

Seems out of a total of 4 ST6's only 1 auto start/anti-space board works.  Can anyone tell me if this is a common problem? In one case, there is a transistor that seems to be in backwards compared the one only board that works. Is it possible this never worked? This board looks like it came from the factory.  Could there have been a substitute transistor used that either had the EBC in a different order?

Thanks all!
Eugene