[GreenKeys] Help with a model 28 KSR Teletype!!!

[tony.podrasky]

GM OMs;

Hello Tom;

The "wildly" thing is when the magnets do not have power applied to
them. The technical term is "Running Open" (i.e. the loop is OPEN
and the Teletype is RUNNING). We used to apply that term to people
who talk and nothing but useless gibberish is coming out.

"What's she talking about? - it makes no sense!"

"Aww - she's just running open again!"

I'm sure someone will post a nice diagram of a loop supply. If I
don't see it by this evening, I'll post one. I have several - but I
don't know if any of them are copyright - so I'll wait.

One thing, if you build your own power supply, is you will need to
put in a resistor to limit the current to the magnets. The magnets
are basically a dead short because their resistance is so low - and
if you connect them directly to a power supply without limiting
the current to 60ma, they will go up in smoke - and really fast too!

Welcome to the group. This is primarily a RTTY group - but you'll find
that the members on here have so many disciplines, that you can ask
just about any question and get an answer.

We even have one guy that launches balloons with a telemetry payload.
I don't recall the altitude - but you can see the earth with a blue
band around it and then blackness. The blue bad being the atmosphere.

UE,
K2EAA - TONY
NNNN
ZCZC

On 12/11/2014 12:41 AM, Baggio, Thomas wrote:
> I have recently acquired a model 28 KSR that I would like to get running
> and connect it to my PC and run the Heavy metal program to get TTY data
> to the Teletype.
>
> I have got the PC part working fine.
>
> When I turn the teletype on with nothing connected to it (as far as a
> current loop supply ) The teletype just turns away wildly.  I believe
> this is supposed to happen.
>
> What I can't figure out is where on the Teletype I would connect the
> output of the Current loop supply.  I have traced the wiring a bit and
> can see that there are two selector Coils wired in parallel with each
> other.  These coils are connected to connector that goes back to a
> terminal strip inside the cabinet.
>
> I guess what I am asking is is there anyone out there that can help me
> with this project.  I am having a very hard time finding any info out
> about how to get this hooked up.
>
> Basically, I want to do the following
>
> from the PC serial port (RS232) I would go into my current loop supply
> that I have constructed using transistors and optcouplers.
>
> I assume because the selector coils are wired in parallel, I need 60 mA
> to  "drive" the coils?  I am not really sure how this works .
>
> DO I just connect the output of the current loop supply right to the
> coil terminals?
>
> It also looks like there is no LESU in this unit. It was used by a local
> HAM radio club in the past.  It looks like they were missing the
> electrical service unit so they bypassed all the  wiring for it.
>
> I really need some help figuring this out.
>
> Any help you could provide or contacts would be greatly appreciated.
>
> I am new to Teletypes and as I understand it, in theory, I need to do
> the following
>
> I think what I am going to do is hook up my current loop driver (I am
> going to try at 20mA so I will need to wire the selector magnets in
> series as they are now in parallel.
>
> My idea is to go in with the current source on one side of the magnets
> .  The current should travel through the selector magnets over to the
> keyboard (signal) contacts, out of the signal contacts over to the
> "negative" side of my current loop.
>
> Does this sound like the basic idea.  I have included a crude diagram of
> how I think it should work.
>
> Thanks in advance
>
> Tom
>
>
>
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