What is a Rotary Phone?

Dial-type telephones belong to the second generation. The call part includes a microphone, a receiver, and an inductor. The signal receiving function is still completed by the AC bell, and the signal sending part is implemented by a mechanical rotary dial. Due to the time-consuming dialing, the chuck rotation is not allowed to be wrong, the pulse contacts are easily damaged, and frequent maintenance and adjustment are needed. They have gradually been replaced by touch-tone telephones ^[1] .

Each cell of the phone dial is a

The dial-type telephone circuit is mainly composed of hook switch H1, H2, polarized bell, dial circuit, call circuit and handle. These five parts are indispensable for any type of dial telephone. ^[3]

The hook switch, AC bell, dial pad and charcoal microphone of a dial-type telephone must be regularly checked and adjusted. The following describes the contents of the inspection adjustment.

1. Hook spring : The reeds should be straight and neat, with a following force, and the reeds should have good insulation. The contacts should be aligned, the pressure between the contacts should not be less than 0.2N, the separation time between the contacts should be not less than 0.3mm, and the contacts should be clean. If there is dirt on the contacts, wipe them off with a rubber sheet or a soft cloth (toothpaste). The pressure plate (or pressure column) of the fork spring should be flexible and the moving parts should be kept clean.

2. AC bell : The armature should be flexible and the moving parts should be clean. There should be a movable gap of about 0.2mm between the armature and the yoke. There should be a 0.1mm gap between the bell hammer and the bell bowl when static. The center of the bell hammer should be knocked on the edge of the bell bowl. The permanent magnet should be firmly fixed.

3 Dial : It can be turned flexibly, and the sound should be soft and no stagnation when turning. There should be a clearance of about 0.2ram between the gears and the turbine vortex rods, and parts with severe wear should be replaced. The inside of the speed governing cup should be clean, and the flying spring should be flexible. The reeds should be straight and follow the force, the contacts should be positive, the pressure between the contacts should be not less than 0.2N, and the gap between the contacts should be not less than 0.3mm. The contacts should be cleaned, and if there is dirt, they can be wiped with a rubber sheet or a soft cloth (stained with toothpaste).

4 Charcoal microphone : The charcoal sand of the charcoal microphone is easy to absorb moisture and stick, which will cause the efficiency of voice transmission to be reduced and the noise will be loud. It is necessary to bake or replace the charcoal sand regularly. ^[4]