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Old 31st Dec 2020, 11:58 am   #1
Xyience
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Default Connecting U43 to an Electric Bell

I have just restored and converted a French U43 Ericsson dated 1964.

I was amazed at just how little I needed to do to get this working on our phone line - a BT line cord, two diodes and a quick clean up of some oxidised contacts.

The sound from the earpiece is a bit quiet and the sound from the Mother-In-Law speaker is about 50% too quiet (any ideas? I might remove the added rectifier to see if this helps - I chose random diodes!)
Apart from this the phone looks and performs really well.

But to the main question - I have a vintage electric bell (see attached) that I would like to use as a bellset for the phone. I know it will not give a traditional twin-bell tone, but this car boot find deserves a purpose in life.

I cannot find much in English on the U43, and nothing about bellsets for the model.
Can anyone suggest a circuit that can connect the two?

[The bell dings nicely with a tired 12V battery, but too aggressively with a 12V 2.5A smoothflow model train supply]

HAPPY NEW YEAR TO US ALL
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Last edited by Xyience; 31st Dec 2020 at 12:05 pm. Reason: attach photo
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Old 31st Dec 2020, 12:41 pm   #2
Dave Moll
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Default Re: Connecting U43 to an Electric Bell

The problem is that the bell shown is a DC trembler bell (rated, as you say, at 12V), whereas the ringing current from a telephone line is 25Hz AC at around 75V or so.

Incidentally, I am unclear what the diodes described are for.
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Old 31st Dec 2020, 12:52 pm   #3
Xyience
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Default Re: Connecting U43 to an Electric Bell

That is an issue. It doesn't sound like compatibility would be easy or cost-effective.

Would the bellset/bell from a junked GPO phone work with the U43? These seem easy to come by.

The diodes are instead of a No 205 rectifier as suggested by https://www.britishtelephones.com/tranchan.htm

Phones are entirely new to me, and I didn't want to blast my families hearing, so I went with the instruction.
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Old 31st Dec 2020, 1:05 pm   #4
Dave Moll
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Default Re: Connecting U43 to an Electric Bell

Quote:
Originally Posted by Xyience View Post
Would the bellset/bell from a junked GPO phone work with the U43? These seem easy to come by.
That sounds like a much better option. You could always use the DC bell as a doorbell.

Quote:
Originally Posted by Xyience View Post
The diodes are instead of a No 205 rectifier as suggested by https://www.britishtelephones.com/tranchan.htm

Phones are entirely new to me, and I didn't want to blast my families hearing, so I went with the instruction.
After posting, I did wonder whether this was what you meant. The way these work is by only conducting above a certain level of signal so that they don't conduct at speech level but the higher-voltage spikes caused by switching are shorted out to prevent "acoustic shock" (loud clicks in the earpiece).
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Old 13th Jan 2021, 11:52 am   #5
Xyience
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Default Re: Connecting U43 to an Electric Bell

I found a perfect donor telephone for my purposes. A stinky, discoloured cream 706. The smell off this phone actually made me gag once or twice!

I stripped off all of the components and mechanical items one by one until I was assured that I had just enough left to operate the bell. This left the metal chassis, the circuit board, but only to mount the striker mechanism, and the two gongs.
I added a resistor to correct the REN and wired up directly to the U43.

This works perfectly. When I get some more time I will give the bellset its own BT plug and add a nice cover to keep fingers away from the exposed terminals. This is hung high up on a wall so it is safe enough for now.
Everyone in the house loves the sound of the metal bells. Takes me right back to the 70's.

I experimented with the phone by taking out the DIY 205 rectifier. This does allow some unpleasant transients to reach the receiver, so the diodes stay.

Thanks for the tips Dave
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