[GreenKeys] Model 15 Electrical and Conceptual Help

[E.]

Out of curiosity, which numbered terminals do the four-prong wire connect to?… that’ll be a good start in helping track down a proper wiring diagram for you.

If it were me, I’d replace the four-pronged cable with SOOW service cable, since it looks like the insulation is breaking down pretty bad near the terminals (could short), but reuse the four-prong plug on the new cable.  I’d also replace the two-prong cable that comes out of the table with a grounded three-prong cord (tie the ground to the metal junction box within the table), but this would be a later project.  Make sure to do hold onto that old two-prong plug though!

If I were to guess (without a diagram)… the table cord powers most AC contained within the table.  The four-prong cable (I can’t tell if there are three or four wires coming out of the cord at the terminals) gets its AC by plugging into the table.  Likely when the M15 *is* plugged into the table, the AC power turns around on one of these prongs — perhaps even switched via the TT and powers that weird two-prong that you see in the table for a rectifier… again, a terminal readout would help.  Be careful not to touch the four prong’s prongs though when plugging/unplugging — it will shock you!

The two DC plugs (looks like operator plugs) that come out of the M15 would plug into the table as color coded.  The three covered terminal strips below the plugs are a pretty standard Bell System layout… you would have to tie two of these terminals together to form a proper loop but as Ken said earlier, you need to put a good resistor (the higher the wattage the better… say 25W, if I remember correctly) on the loop to bring down the DC amperage for the selector magnets -- or else no more Teletype!  Since this is DC, you would need a 120VDC rectifier and I do have a suggestion where you could get one… please just let me know if you need it.

I’ve found a diagram that might apply to your situation… hope it helps and good luck :) !

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> On Aug 5, 2026, at 5:40 PM, Thomas McCourt via GreenKeys <greenkeys at mailman.qth.net> wrote:
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> 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?
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> 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
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