BELLSET No. 21

Used when a CB telephone could not achieve current when on a long line of high resistance.  This Bellset used a local battery, to power the telephone transmitter.

Used on the following systems (1928):-

1. For C.B., C.B.S., Nos. 2 and 3, or magneto systems; with Telephone No. 154 or No. 196LB.  Diagram C.B. 1333.
2. For C.B.S. No. 1 systems; with Telephone No. 154.  Diagram C.B.S. 559 or N1296.
3. For automatic systems; with Telephone 156LB.  Diagram A.T. 1872.

Used on the following telephones (1946):-
For use with Telephones, Nos. 154, 156LB, 196LB and l/196LB.

There were variations of this Bellset: Mark 234 (8 terminals) and Mark 3 (12 terminals).

Superseded by the Bellset No. 31.

Bellset Mark 234 includes (1928):-
1 x Bell, No. 1A, unmounted.
1 x Coil, Induction No. 15.
1 x Condenser, M.C. No. 30 2uf.
1 x Case No. 1.

Bellset Mark 3 includes (1946 and 1956):-
1 x Bell No. 1A, Unmounted.
1 x Clip No. 14.
1 x Bell-gong No. 2, Oxidized.
1 x Bell-gong No. 2A, Oxidized.
1 x Coil, Induction No. 21A.
1 x Condenser, M.C. No. 102.
1 x Case No.1.

Circuit diagram - N521.

Drawing - 63015 (Mark 3).

Picture taken in 1929.

Adjustment of Magneto bells

Last revised: July 30, 2025