[GreenKeys] Model 28 signal lines

[Ralph Mowery]

I have only had 28 for a short time, so may be talking out of my hat.

 

I ran an experiment  just to see.  This unit has the polar relay or whatever and does not key magnets  directly .   I ran a couple of lines of RYs  using only a supply of about 12 volts (adjusted to give 60 ma) and a 50 ohm series resistor, then I took the resistor out of the line and it took slightly over 8 volts to give 60 ma.  

 

Both voltages gave me perfect copy off the keyboard of 2 lines each of the RYs and then some random typing I did.

 

Now if this had been the model 15 series like I have 50 volts just start to try and work.  It takes around 75 or more volts to make it run correctly on a local loop and more is better if I run it on a radio receiver and demodulator.

 

I have not had time to check out the 28 on the radio or anything but a local loop.

 

For the original poster, you can set the supply to give you about 20 ma.  You may have to try both ways with the plus and minus wires .  If the machine quiets running open and quitens down at 20 ma it is probably set for 20 ma.  If it still runs open, then do the same with more current and see if it quiets down at about 50 ma.  If so, then it is a 60 ma machine. 

 

Ralph ku4pt

 

 

 

From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Paul Heller
Sent: Wednesday, October 16, 2019 6:20 PM
To: B M
Cc: GreenKeys at mailman.qth.net
Subject: Re: [GreenKeys] Model 28 signal lines

 

Barry,

 

My only point, and others may disagree, is that 48v is not enough. 

Paul
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On Oct 16, 2019, at 4:10 PM, B M <iamvirtual at gmail.com> wrote:



Many thanks to all that replied. Now that I know it is necessary to confirm the options that might be in place, I can look closely at my machine and compare against the manuals to determine what I need to do.

 

Thanks!

 

--barrym

 

On Tue, Oct 15, 2019, 12:28 B M, <iamvirtual at gmail.com> wrote:

I took a look through the theory & operation manual for the Teletype Model 28 KSR (floor standing model), but I am still confused on where the signal lines in and out are located.  I do see the 2 terminal strips at the back of the cabinet with labels from 1-20 and 21-40.

 

I have a few questions

1. which terminals are for the signal lines in?

2. which terminals are for the signal lines out?

3. how do I determine that the unit is still set to use 60ma loop?

4. will 48v @ 60ma be sufficient to drive the model 28 KSR?

 

As you can see, I am not familiar with Teletypes. 

 

Any help would be greatly appreciated!

 

Thanks

 

--barrym

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