Wall mounted switch unit, with bell ringer, for extension plans 5 & 7 on CBS No. 1 systems and fitted close to the main telephone.

For one exchange line and one or two extensions with intercommunication (only during an exchange line transfer), with or without secrecy.

On the side of the case is a night service switch which disconnects the local bell.

Used with Telephones No. 3 and 9 on C.B.S. No. 1 Extension Plan No. 7.  Latterly used with Telephones No. 156 and 196.

The later version consists of a wooden "Case No. 2", fitted with ringing generator, four position switch, indicator and magneto bell.

There are two cases used, the earlier case being fitted with a key lock and higher than the one shown in the pictures.

The wooden cases were specified to be of well seasoned American Walnut, (or as an alternative, one of  the following woods of Imperial origin known as Pyinma, Black Chuglam, Haldu, or Tasmanian Myrtle, may be used provided it is stained to match American Walnut as closely as possible before being polished).

All external metal parts were plated with Copper Oxide and lacquered.

Introduced in 1923.

Diagram - N507.

Drawing - 7115 (Mark 236).

Specification - S27.

Bellset includes (1928):-
Refer to table below.

  Mark 234 Mark 235 Mark 236
Diagram number CBS189 CBS257 CBS500
Bell No. 1A, unmounted (with two Bell-gongs No. 17) 1 1 1
Condenser, M.C., No. 1 - - 1
Generator No. 4C 1 1 1
Indicator and Key No. 3 1 - -
Indicator and Key No. 5 - 1 -
Indicator and Key No. 9 - - 1

Adjustment of Magneto bells

Bellset No. 7 (Mark 236)


Bellset No. 7 interior



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Last revised: October 17, 2023