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
Close up of the rod
Close up of the rod and spring
Last revised: May 24, 2022