I recently got myself a GPO 746. A very old rotary dial pulse dialling type telephone.
Usually, to dial a number you just put your finger in the hole and turn it. HOWEVER. The thing doesn't "turn back" correctly. It'll give a pickup as if I just picked up the phone again. I think this is because it's not going back as fast as it should.
If I pull a number and push it back into position manually, a bit faster. It'll dial that number! So I think the retaining springs inside are a bit loose. Would anyone here know how I could either tighten this spring or would I have to get a new spring?
There is usually a 'bucket and weight' centrifugal governor on the dial return, which is worm driven. The end float of the shaft is adjustable with a screw, and I have known this to be over-tightened by people such that the governor is too tight for the return spring to move it. Likewise, if the grease on the governor drive and bearings has gone hard and sticky, this can also jam or restrict it.
The dial assembly is easily removed to work on it. There is a single screw at the bottom, which needs only to be loosened. The dial then hinges up and away from its mounting cradle at the bottom, and then lifts out at the top. The dial return speed can be checked, once you have it on the move again, by dialing a zero, and then saying out loud "One-thousand-one-hundred-and-one". That's without any gaps in the words and just at normal talking speed.
The dial should hit stop just as you finish speaking. The exchanges are ( certainly used to be ) fairly tolerant of the pulse repetition speed, but if it is too far out, a mis-dial can occur. If the spring is broken , it usually goes at the looped end-anchor. By heating it in a gas flame, you might be able to bend a new anchor on it. The other option might be to use a section of an old clock mainspring.
It's been a long time since I worked on one of these, so it's all from memory, but I think I'm about right. Hope it helps.
Return time from Zero dialing to rest position should be about 1.1 seconds in America and I think is a bit different in Europe. I remember tone pulses at 10 pulses/second.
I think you should clean the inside clutch which makes uniform return rather than tighten spring and adjust the press screw to get this rate.
This is probabbly the best site for old UK phone info
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Circuit etc.
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Dial type 21 (basically the type 12 dial with plastic case and clear finger plate)
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When a rotary dial has been unused for years it will generally become slower in operation (or not work at all) due to lubrication drying out, or somebody has played around with the tensioning of the governor arms (or both). The only way to fix it is to totally strip it and then re-assemble. This means you have to know what you are doing and how to set it up and adjust it if it is to work properly. Techs in training usually spent a week performing this operation under supervision before they became proficient at dial refurbishment.
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