INDICATORS No. 3501AN and 3701AN
Used when loud bells, that required their own DC power source were required, in subscribers premises.  Any original bell would be replaced by the Indicator which consisted of a wooden case with a switch and indicator.

The Indicator is the drop flap type, which will drop on an incoming call.  A local DC bell with batteries is provided and the bell is operated by a contact in the indicator.  The bell can be switched on off by the switch on the front panel.  The indicator flap is restored by hand.

Indicator No. 3501AN was used on CB and Automatic lines.
Indicator No. 3701AN was used on CBS No's 1, 2 and 3 and Magneto lines.

The only difference between the two variants is that the Indicator No. 3701AN, has a double wound coil of 500ohms and 500ohms with a centre tap.  The Indicator No. 3501AN has a single coil of 1000ohms.

Introduced circa 1933.

Indicator comprises:-
2 x Capacitor, M.C. No. 101.
1 x Indicator No. 3500A (3501AN) or Indicator No. 3700A (3701AN).
1 x Switch, Tumbler No. 20.
1 x Tag No. 47.
1 x Wooden case.

Indicator No. 3501AN was superseded by Indicator No. 4001AN and Indicator No. 3701AN by the Indicator No. 2201AQ.

Diagram - N1283.

Drawings - 9813 and 9814.

 

 
 
BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find All Telephone Systems
Last revised: December 04, 2025

FM