:On Sep 21, 6:02 pm, Ross Herbert wrote: :> On Wed, 16 Sep 2009 17:31:23 -0700 (PDT), Bill Bowden :> wrote: :>
:> :On Sep 15, 7:49 pm, Tim Williams wrote: :> :> On Sep 15, 8:35 pm, George Herold wrote: :> :>
:> :> > So Bill I really know nothing about old phones, but if you want to :> :> > find the resonant frequency, just hit the system with a delta :> :> > function. (ping the gonger?) and the frequency it rings at is the :> :> > resonant frequency. :> :>
:> :> Ah, but it's a nonlinear system -- nothing happens until it hits a :> :> bell, which takes some energy out, then it swings over and hits the :> :> other, etc. A lot like putting a diode to +V and a diode to -V around :> :> a parallel resonant tank -- everything goes fine and dandy until it :> :> smacks into a rail. :> :>
:> :> I might suggest getting a 20Hz generator (motor plus another phone's :> :> dynamo??) and tweak it while running. :> :>
:> :> Tim :> : :> :Yes, you see the problem that nothing happens until it hits a bell :> :which knocks everything out of sync with erratic results, but maybe :> :that's the way it was designed? :> : :> :The ringer is just for display and will not be connected to the phone :> :line. I built a :> :driver circuit using a square wave at about 20Hz to simulate the :> :action. I wired the 2 coils in parallel to reduce the required :> :voltage, and bypassed the capacitor so the mechanism operates fairly :> :well at 20 volts AC. I tried varying the drive voltage and frequency :> :from about 10 volts to 24 volts without much change in action. It :> :seems to work the best at about 20 Hz and 20 VAC. :> : :> :I could remove the bells and tune the thing for maximum swing of the :> :gonger at lowest voltage, and possibly find a resonant point, but that :> :probably won't help when the bells are replaced and the whole :> :situation changes. :> : :> :-Bill :>
:> As KosephKK has said "you mucked the circuit". :>
:> the ringer is a magnetically polarised device and the windings are designed for :> series operation such that the polarity of each coil on successive half cycles :> aids one pole while repelling the other. You can't connect the windings in :> parallel and expect it to work. Also the voltage must be at least 40Vac for :> effective operation. Real worl exchange ringing machines for ringing bells like :> this were nominally 90Vac rms and the waveform was quite peaky. : :I don't see why it should matter if the windings are in series or :parallel, since the magnetic phasing can be changed by reversing the :connections to either winding. So, there are 2 possible ways to :connect the windings in parallel, and only one arrangement works. : :Yes, I imagine the voltage was fairly high using a cap in series.The :cap measures 1uF which has a reactance of about 8000 ohms at 20 Hz. :which drops most of the voltage. But the cap isn't needed since it :won't be connected to the phone line. The ringer operates somewhat :from a 5 volt peak sinewave from a function generator connected :directly to the parallel windings. But I still can't find a mechanical :resonant point. : :-Bill
Upon reflecting, you are correct that a parallel connection with correct phasing will do the same thing. However, the sensitivity of the bell will be markedly reduced since the current requirement to produce the same magnetic effect will increase.
I don't know why you are having such a problem in getting the bell to operate correctly. If you feed it the right frequency and voltage it is very simple to adjust for maximum effectiveness. A 5V sinewave is just too low in amplitude and anyway, such bells respond better if the ac waveform has a rather peaked waveform. When I was a trainee tech learning about magneto phones the instructor always reminded us that the shape of the armature of the hand turned magneto was specifically designed to produce a "spiked" waveform because the bells would then receive an initial "kick" to overcome the magnetic bias and the gongs would be struck slightly harder than if a pure sinewave were used.
Here are a couple of links on magneto bells which might help.