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neighmond, The "master relay" or R-1 is of two varities made for 24 volt service.
The most common IBM/ITR R-1 used in US domestic impulse wind master has an alternating current relay coil, and usually has a copper dampening ring around the electromagnet core. The actual relay has heavy-duty contacts. The relay was generally held by wood screws on rubber gromets because they tend to be "buzzy."
A similarly made relay but with a DC only coil was used on IBM/ITR master clocks as R-1 on those made to be used with a local DC battery source.
On many, R-1 is replaced nicely with a noiseless solid-state relay of appropriate capacity.
It is important to replace R-1 with the proper type.
It had a DC one way back when I scrounged the box, and I found a small Potter Brumfield one that is AC that works after some minor rewiring but it is at the end of its life (was old when I found it.) I got a real nice filtered power supply from the telephone company that has both rectified and AC so either will work; the relay is in a glass fronted case with five other ones so that was why I was hoping someone would have one that would look pretty close.
Neighmond I have about a dozen old relays but without more to identify which I don't know if I can help. If you could contact me with more info and maybe a picture I will be glad to check through what I have. My email is firstname.lastname@example.org.