In situations where bell tinkle was produced on customer telephone installations a bias spring was fitted to 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 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.
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.
After this date no new Bells were produced with Bias Springs pre-installed.
Bell No. 1A unmounted with Bias Spring
The Bias Spring is the right of the picture
Last revised: December 02, 2020