[GreenKeys] New to real Teletype

[Dave G4UGM]

1. You don't need a TU to do local printing but you do need a "loop supply"
to operate the printer solenoids

2. The keyboard simply operates a changeover switch which is usually used to
reverse the polarity of the loop.
In order to get "local echo" you need connect the loop supply through the
keyboard switch and the selector
Magnets. The keyboard will reverse the polarity of the flow in the magnets
and generate printing.
You also need a series resistor to limit the current to 60ma. It is
necessary to use a high voltage supply 
Due to the high inductance of the selector coils.

3. It is pretty common to by-pass all the switching in a TTY as usually the
TU provides change over controller..

Perhaps take a look at this. It talks about Creed's but the Model 28 works
in a similar way...

http://www.baudot.net/creed/docs-alan-hobbs/rtty-the-easy-way.pdf

Oh looking at the tech data sheet for the Model 28 it may have a loop supply
hidden in it somewhere.

http://www.samhallas.co.uk/repository/telegraph/teletype_28_tech_data.pdf

and 65ohms sounds right for the selector magnet, the above sheet quotes
66ohms.

4. Receiving off the air can be done in many ways. Lets get local loop
working first

Dave
G4UGM


> -----Original Message-----
> From: GreenKeys [mailto:greenkeys-bounces at mailman.qth.net] On Behalf
> Of Trent Williams
> Sent: 18 October 2015 23:33
> To: greenkeys at mailman.qth.net
> Subject: [GreenKeys] New to real Teletype
> 
> Hello from KJ4KAF,
> Yesterday, I brought home a model 28 KSR.  The seller (ham operator) gave
> me a good demonstration of the printing function as a signal was fed from
an
> ST-6. However, the keyboard function is not connected to anything it
seems.
> The keys do function and there is mechanical action when a key is pressed.
> 
> His signal feed line appears to bypass almost everything and connects
directly
> to the 2 solenoids (wired in parallel). The line has around 65 ohms of
> resistance.
> 
> Is there a way to have the machine print what I type? Is an ST-6 what I
need
> as well?  My first goal is to receive anything I can find on the bands or
the
> Internet. At some point, I would like to at least print what I am typing -
will
> the right TU do this?
> 
> This is the first teletype I have ever seen - what an incredible
mechanical
> wonder this thing is!
> Today, I just signed up to join the email list.
> 
> Thanks for any help understanding this, Trent
> 
> Sent from my iPad.
> 
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