[GreenKeys] Model 15 Electrical and Conceptual Help

Thu Aug 6 18:05:11 EDT 2026

Thomas,

Welcome to Greenkeys and the world of mechanical digital communications!

The Teletype Corp. Model 15 used both 120 VDC and 120 VAC, so to keep 
them apart, the table was designed with different types of plugs. You 
may want to just ignore the interconnect box under the table and wire 
things directly. A schematic of box enclosed - should be similar to what 
you have.   For the motor, you can just use a standard 120 VAC, 3-prong 
(grounded) plug, wired to terminals 21 & 23 on the terminal block.

Electrically, the keyboard consists of 6 sets of contacts (bits 1-5, 
plus the STOP contact), all in parallel. In standby mode, the STOP 
contacts will be closed.

Electrically, the printer consists of an electromagnet, known as the 
"Selector Magnet." This electromagnet is made up of two windings or 
coils, usually wired in parallel (60 ma. loop). It can also be wired in 
series (20 ma. loop).

Normally, the keyboard and selector magnet of one unit is wired in 
series with the keyboard and selector magnet of a second unit, with a 
current limited power supply providing the 60 (or 20) ma current.  This 
is know as a "current loop" and is the same as was used with telegraph 
equipment.  See  "54 TTY loop" enclosed. Typically, for a 60 ma. loop, a 
supply of 120VDC with a 2000 ohm series, current limiting, resistor is used.

If you are mainly interested in connecting the M15 to a computer, there 
are 20 ma. loop to RS-232 adapters that you may be able to find.  But be 
aware that modern, USB, serial ports will not go slow enough for a 
teletypewriter! These machines only operate at 45 baud.

Did you know that y our M15 can play music?
See https://www.youtube.com/watch?v=pDy60HDr558

Hope this helps,

Duncan Brown, K2OEQ
USASA    31J30

Antique Wireless Association
  Communication Technologies Museum
    Asst. Curator, Commercial Equipment
(also chief TTY op & repairman)

i-Telex: 212503

www.antiquewireless.org

AWA Youtube channel: 
https://www.youtube.com/channel/UCX55peBhzeX1qps_VYXdLBA

Virtual AWA Museum TTY Tour: https://www.youtube.com/watch?v=TpB6jM90VV8

On 8/5/2026 6:40 PM, Thomas McCourt via GreenKeys wrote:
>
>
>
> Hello greenkeys, my name is Thomas, and I am a chemical engineering 
> junior who has been interested in mechanical calculators and teletypes 
> for a number of years. I was just able to acquire a model 15 off 
> facebook marketplace about a month ago. From my experience with 
> messing around with typewriters and my Friden calculators I feel 
> pretty confident that I can figure out working with the mechanical 
> side of the model 15, but I'm entirely out of my depth on the 
> electrical side of things. How electrical stuff works on a fundamental 
> level has been entirely non intuitive for me and is the reason I 
> didn't go for ECE, and I simply don't know what I don't know. I don't 
> want to fry components of this thing, so I'm here.
>
> I've done some research and I've watched all of the Curious Marc 
> videos where he restores a 19 and a 15, and I've downloaded and 
> started to read the manuals he archived. I also tried looking through 
> the archives of greenkeys, but I didn't see any way of sorting it 
> by topic. I still tried looking through 1.5 years of the subjects, but 
> I didn't see anything which applied to my situation.
>
> My 15 came wired up with a 4 prong plug where 3 of the prongs are 
> parallel and the other is perpendicular to the others. It also came 
> with a stand which had 2 2 prong wall outlets, the 4 prong, some large 
> 2 prong I've never seen, and ports for the send and receive. The stand 
> itself had a male 2 prong plug. The last time this was used seems to 
> be in 1958 in a hospital based on the paperwork that was under the stand.
>
> With all of that said, I'll ask my questions. Can the 15 be wired such 
> that it can be plugged into a standard US outlet without the stand 
> using a normal plug? From looking at a wiring diagram which looks like 
> it matches I think it says that it can take 110V AC from the 4 prong 
> plug, or 120V DC from a different plug. Next, how do I set up a 
> current loop so it can just print to itself? What do I need to 
> buy/build to be able to connect a computer to it? With the photo I 
> hopefully attached correctly, what are the intended purposes of the 
> ports under the stand? What are things I should be especially 
> careful of when working on this, in any sense?
>
> Sorry for all of the questions and text, but I wasn't able to figure 
> this stuff out from my research thus far,
> Thomas M
>
>
> 20260707_170540.jpg
> 20260707_170548.jpg
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>
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