Jack Unit No. 1A and 1B
The unit comprises of a telephone circuit similar to that of any 700 type telephone, except that it obviously does not have switch hooks, handset or a dial.
The Jack Unit No. 1B is similar to the 1A except it has a printed circuit board and a Regulator No. 6B fitted.
Generally, these were used on Key and Lamp units, exchange supervisors desk etc.
Last revised: March 02, 2021