Australian Post Office
Telephone No. 8501 and 8521

The telephone is a Type 8501 and the plinth the Type 8521.  This is an intermediate telephone that can has one or two extensions connected to it.

The switching unit comprises a buzzer, relay, lights and switch unit.

The unit requires 24v DC to power it.

Probably the successor to the Type 271.

The buzzer is for internal communication, whilst the bell in the telephone indicated incoming exchange calls.

Available in grey only.

The GPO had a similar arrangement which comprised of a telephone fitted on top of a switching plinth.  This was called the Planset N625, which is different to this type, but some of the parts including the switching set itself are identical.  The Planset N625 was made by GEC.

Type 8521 circuit diagram

Connections:-
24v Positive - Red wire of cord
24v Negative - Black wire of cord
Exchange line - Blue of line cord
Exchange line -Blue/White of line cord

The keys are used as follows:-
Release - This key releases the keys to the right of it, which are locked down when depressed
Speak to exchange - Pressed when the main telephone is connected to the exchange line
Speak to extension, exchange held - Pressed when the main telephone enquires of an extension whilst on an exchange call
Extension to exchange - Connects the extensions to the exchange line
Ring 1 - Rings the buzzer in Extension 1
Ring 2 - Rings the buzzer in extension 2

To the right are two lamps, which are associated with the two right hand keys

Connector plug at the end of the plinth cord

Last revised June 17, 2025

FM2