In situations where bell tinkle was produced on customer telephone installations a bias spring was fitted in the Bellsets used on site.  In most instances the GPO knew what combination of equipment could cause bell tinkle and certain Bellsets were produced with a bias spring included as standard.

Originally, on the "Bell No. 1A, unmounted", the bias spring was a spiral spring fixed to the bell ringer frame at one end and the other end attached to an arm fixed to the armature.  The frame actually just has a hole drilled through it and what looks like a slot headed screw is in fact a two pronged pin, which is a push fit into the drilled hole.

Fitting a bias spring on an existing bell ringer was obviously not an easy task for field staff and a "Bell No. 1A, unmounted, with Bias Spring" was made available as a replacement part.

Around 1934 a new standard bell ringer, the "Bell No. 59A, unmounted", was introduced and obviously a bias spring may be required.

Two new bias springs were also introduced,  Part 1/SSP/593 was for use on the "Bell No. 1A unmounted" and Part 2/SSP/593 was for the "Bell No. 59A unmounted".  These were a much simpler flat metal strip which could be retrofitted easily to existing bell ringers (see pictures below).

After 1934 no bells were supplied with bias springs pre-installed.

Bell No. 1A unmounted with Bias Spring

The Bias Spring is the right of the picture
The frame is drilled to accept the slot headed fixing pin and the armature is also drilled to accept the extended rod

Close up of the rod

Close up of the rod and spring


Part 1/SSP/593


Part 2/SSP/593



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Last revised: May 24, 2022