[GreenKeys] M28ASR Wiring

[w9ddd at tapr.org]

Sure does open the door.  And I can muddy the waters if I get long

Everything below is in reference M28 series only.

First, from memory (because my antique Apple devices don't do a good job job of displaying PDFs).

A standard LESU presumes the loop to to be on A-5 and A-6, so if it was your intent to mimic standard wiring, your right side jumpers aren't quite right.  A 5&6 go to C 7&8 where a whole bunch more jumpering goes on.  Do you have a line relay or not etc.

Series connection of selector magnet for 60 nA isn't standard practice.  I have to add that it's 6 am here and I may have misread what you said.

A lot of times the chart for changing between series and parallel wiring is off in the notes somewhere to the left or the bottom of the drawing sheet.

Selector magnet wiring configuration for the typing units was done on the A strip until they got into crticom and tempest sets.  I have an LP77 that has the strapping at the selector magnet like the reperforators. 

Now to muddy the waters.

How did we end up with two different values for loop current?  I can image early on it took 60 mA to the sounders.  Then as they got more sensitive a lower current would result in extended battery life. I also read references to 30 and 65 mA loops.  30 would seem to be more logical for series connection than 20.

I have always removed line relays from 28 KSR/RO LESUs on the theory that it's an additional point of failure.  Amateur literature seems to center on 60 mA loops, so that's what I've always used.  The TU-170 is designed to provide 60 mA only.  And the default for others seems to be 60.

Now when it comes the ASR I was kindly gifted I haven't decided for sure, but I will probably leave the line relay it because it's tightly integrated into a circuit that allows printing local copy while punching tape.

John, W9DDD


> On Dec 24, 2020, at 4:18 AM, Steve Garrison <steve.n4tty at gmail.com> wrote:
> 
> Some updates!
>  
> I have now seen some notes about 20mA vs 60mA operational changes that had to do with some wiring changes in the line relay and line test switch areas.
>  
> But I think I am going to just by-pass all that and wire the A-Block as shown in the two attached pics.  One for 60mA and the other for 20mA.
>  
> Anyone with any comments.  Boy does that open the door!
>  
> Steve G./N4TTY
>  
> <A-Block60mA.JPG>
> <A-Block20mA.JPG>
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