Common Audible unit for keyless 3 line phones

[Babybearjs]

I was looking at the S.C. paperwork for the old 3 line keyless phones and remembered that it was the only unit that used Zener diodes instead of vacuum tubes... heres my question: has anyone ever tried to remake this unit for use.... I'd like to know if it worked.... just like the original units that has tubes, it uses a earth ground... has anyone ever tried to make one using a buzzer, or would it have to be a high voltage buzzer?? and what about the z-diode?? what part number would it be?