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Old style UK phone to ring


redcarpet1956

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Hi

I have an old style rotary-dial UK telephone that I want to use as a live prop on stage.

Does anybody know what voltage I must send down the line to make it ring?

Also which core of the 4-core cable to use?

Also which polarity?

 

I played around with these old phones many years ago and I have a feeling it is something like 48 volts but I can't quite remember and I wonder if anybody else has done this?

 

I don't want to use a sound file - I want to use the real thing.

 

Thank very much

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50v at 20 hz I seem recall,the hardest bit is getting the ringing pattern correct.

 

 

 

Ah ha - 50v - I thought it was around there - thanks very much.

I agree about the ringing pattern problem though.

I had thought about trying something out with a sbc or arduino or something but it would get too complicated as I want the phone to stop ringing when somebody picks up the receiver, so I will stick to the manual mode.

 

Thanks for your speedy reply though.

 

All the best

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One of these is always good to have

 

http://www.ebay.co.uk/itm/Vintage-Bakelite-Magneto-Generator-/371928342525?hash=item5698a81ffd:g:VDkAAOSwSlBYuDl0

 

same vendor (no connection or endorsement) also has field telephones with built in generators

 

Often real phones are disappointingly quiet on stage, stand them on a large biscuit tin as a resonator, or even mic it

 

FleaBay has plenty of vintage UK phones GPO, type 300, are good keywords to search

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For many years I've just used a 48v transformer and a push button. You have to adjust the gongs for the bell to work at 50hz but no-one has ever commented that it doesn't sound right.

 

Rewire the phone so that lifting the receiver does not stop the bell ringing - the talent are very good at not replacing the receiver properly and that can be a problem if the phone needs to ring again!

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Probably easier to do this with a small speaker and a sound effect played in.

But bells (typically) sound terrible like this. MUCH better to do it for real. I made a ringer many years ago (not my design) that did UK and US cadence, stopped when phone off hook, etc. If I wanted to do it now, I think I'd do as Brian suggests.
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In the UK, the ring is 80V AC (at source). The idle "on hook" voltage is -48V DC across the A/B pair (A=0V, B=minus 48V).

 

The cadence for the UK is 400ms on - 200ms off - 400ms on - 2s off. For the US it's 2s on - 4s off; this cadence is also often used on UK PABX systems for an "internal" call.

 

 

Kevin

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Tom Engdahl's ePanorama.net has a lot of useful stuff about telephones.

 

In true Blue Peter style, here's one I made earlier:

 

Schematic

Source code

Hex file for programming

 

The amplifier stage doesn't seem to work but you can tap-off the ring signal and use an external amp, which is what I did when it was needed for a prop. I might be able to find a blank PCB and a programmed chip if it helps.

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The amplifier stage doesn't seem to work...

 

Hi John,

 

the biasing arrangement feeding pin 8 of the TDA1905 looks a bit odd. The chip seems to sort itself out (if look at the internal circuit there is a bias arrangement already feeding pin 8) for running on a single rail supply.

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The amplifier stage doesn't seem to work...

 

Hi John,

 

the biasing arrangement feeding pin 8 of the TDA1905 looks a bit odd. The chip seems to sort itself out (if look at the internal circuit there is a bias arrangement already feeding pin 8) for running on a single rail supply.

 

Thanks Brian. The time scale was too short to be able to spend much time trying to sort it out, but it worked perfectly with an external amplifier feeding back to the on-board resistor-transformer-resistor combination. I think the buffer stage isn't really required. I need to sort it out as we want one for our local Heritage Museum to try and resurrect the old telephone switchboard.

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