Sorry for the typo, yes its a ITT 501 KSU.....


Sam: If I remember correctly, the person who built the ITT 501 me said for some reason he was unable to get the teltone unit to work right without the manual intercom card but I could be wrong......


I think I am getting the hang of color code and pins to terminate on the punch down block for the key sets at the top and what needs to be punched down for the incoming phone lines at the bottom of the block.

Only part that I don't understand what color/pins that needs to be terminated for the audible signal part of the punch down block from B1 to CA . As the Bell System Practice that I looked at did not have the color or pin.

If any one has a color chart or a close up photo of the 551B KSU, that would be very helpful.

Thank you all of you for all your help and understanding.