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

Thu Dec 11 13:24:56 EST 2014

Tom, look at the upper left-hand corner of my diagram, here: 
http://ai2q.org/rtty/tu1.htm

The loop supply is built in on my Model 28.

Vy 73, AI2Q, Alex

Member: ARRL, FOC, RSGB, CWops, QRP-L, Antique Wireless Association, the 
Southern Maine Area Amateur Radio Team (formerly the New England Radio 
Discussion Society), DXCC Honor Roll, 16ØM DXCC, 8ØM DXCC
http://ai2q.org

----- Original Message ----- 
From: "tony.podrasky" <tony.podrasky at gmail.com>
To: <greenkeys at mailman.qth.net>
Sent: Thursday, December 11, 2014 11:33 AM
Subject: Re: [GreenKeys] Help with a model 28 KSR Teletype!!!

> 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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>
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