Convert Magneto Telephone Bells into Doorbell

[slderiron]

I recently got the bell box (pictured) with a pair of magneto phones. With the help of this forum I have the phones set up and working well. However I was in a mind to convert the bell box which is surplus to requirements, into a door bell.

I connected various batteries to the terminals but with no luck, until I noticed on the diagram that a bias spring needs to be fitted to the right handside of the coils, presumably because the DC current will only make the gong go in one direction, and the additional spring would pull the gong back in the other direction. Am I right about this?

This being the case I'd be grateful if anyone has the correct armature and spring available.... failing that I may have to cobble something together

[AndiiT]

Hi,
A magneto bell such as yours is designed to operate on AC current and not DC. To use the bell as a doorbell you would need to find a suitable low voltage AC source in order to make the bell operate.

Regards
Andrew

[russell_w_b]

Originally Posted by slderiron

I recently got the bell box (pictured) with a pair of magneto phones. With the help of this forum I have the phones set up and working well. However I was in a mind to convert the bell box which is surplus to requirements, into a door bell.

You could knock up a little circuit like the one shown in this post!

[dagskarlsen]

If I dont remember wrong, you had a spare generator too. Just put it up instead of the ringer button, and you have the ideal ringer powersupply too.

It may be possible to tune it to ring at 50 Hz, too adjusting the clapper to shorter moves, and following up with adjusting the bells. A transformer supplying 40-50 V should be fine. A capacitor of 1-2 microfarad in series with the transformer (40-50V side) will protect the circuit.

dsk

[slderiron]

Thanks for the advice. I think I might not use this old bell box as a door bell, it seems more problematical than I first thought. I'd have to give the crank handle prutruding through the door idea a miss as it would look more than a little odd. If I was to wire it up to the mains then I'd need to use a pretty hefty resistor in place somewhere in the circuit, though it seems this would be the proper way forward, but I'm unsure what rated resistor to use.

With regards the magneto, it barely seems to chuck out 1 volt when I tested it with the multimeter, though it seems to ring the bells quite well, so I'm not sure it has enough whack left in it to use on a toilet seat .

I think I'll wait for one of those bakelite GEC doorbells to become available as I wouldn't have to tinker with one that already works. Regards, john.

[AndiiT]

Hi,
I wouldn't recommend connecting the bell to the mains via a resistor for a number of reasons, not least the problem of finding a suitably rated bell push.

If you were to go down the route of using your magneto bell as a doorbell you would at the very minimum require a double wound (i.e. not auto) transformer to reduce the mains voltage to somewhere around 40 to 50 Volts.

Did you check your magneto output on the DC or AC range of your multimeter?

Regards
Andrew

[slderiron]

I've learned quite a bit regarding magnetos on this thread, a simple google and I learn that magnetos work on AC current and there's me messing about with batteries.
This magneto has a current in the range of 17-22 volts, is this about right?
Do meggers work in the same way? I've seen 500v and 1000v types of these, bakelite examples which I've considered buying but it occurs to me that if they're capable of chucking out that sort of voltage they would be quite hazardous. Regards, john.

[russell_w_b]

Originally Posted by slderiron

Do meggers work in the same way?

No.

A d.c. 'Megger' provides direct current and contains a dynamo and commutator to obtain d.c, typically at 1,000V, 500V, or 250V to pressure-test circuits at a d.c. voltage twice the rated circuit voltage. A slipping clutch ensures constant output.

a telephone magneto is a simple two-pole slip-ring device that provides non-sinusoidal a.c. at, typically 75V RMS (although the magnetos on my Soviet field telephones give out 200V RMS with some enthusiastic cranking!). Normal, steady rotation will provide this voltage at a frequency of about 17Hz.

Attached is some magneto stuff (type 26A).

[Herald1360]

I wonder whether a "normal" dc bell sans gong or even a relay with a normally closed contact could be used as a crude vibrator to drive a small mains tansformer backwards to generate sufficient LF AC to operate the magneto bell. The relay approach wouldn't take up much space, a second contact could be used to actually switch the dc into the transformer and you could safely use an ordinary bell push to control it.

I feel a tinker coming on with an old telephone.....

[russell_w_b]

Originally Posted by Herald1360

I wonder whether a "normal" dc bell sans gong or even a relay with a normally closed contact could be used as a crude vibrator to drive a small mains transformer backwards to generate sufficient LF AC to operate the magneto bell.

It should do, because the GPO had a similar method to what you describe! I once used the self-same arrangement with an octal relay to drive an induction-coil. You'll need a bit of C across the contacts or they'll pit and burn, resulting in irregular ringing.

I feel a tinker coming on with an old telephone.....

The difference between what I expect you'll tinker with (type 59A bellset) and the Bell from the OPs 'Bell-Set No:1' is that the Bell-Set No:1 is designed to work from 16⅔ Hz, (as opposed to 25Hz) and can't easily be adjusted to work at, say, 50Hz as a type 59A bell-motor can.

Suitable vibratory adjustment ought to do the trick, though, and I think the electric bell method would work better than a relay here. The electronic circuit I put up in post #3 isn't really that difficult to knock up, and can be made easily with salvageable parts; the transformer doesn't even need to be centre-tapped - a couple of secondary taps will do with the mid-point between them used as a centre-tap. All I would suggest is experimenting with the transformer to get the frequency within parish.

[Julius22]

Maybe you could use an "old" internet modem to supply the ringing voltage.

[Maestro Maker]

Hi
All this rings a bell . . .

When I got married in 1949 we had rooms in wifes parents Edwardian house that had been lit by town gas but "had the electric put in" in the late 1930s; very upmarket cooker etc.
But the doorbell was a lovely mahogany ringer box run straight off the mains via a very stout pushbutton in the porch.
What I at first thought was a tranformer turned out to be an unusual style fuse box.
When the bells rang they would waken the dead!!
The family took a dim view of the quieter Freidland replacement.
I was told a relative had been a PO telephone man.

Cheers, MM