Old Telephone bell(?) to be used as a doorbell

[BOC]

Hi

I need some help with a bell that I've bought that i want to use as a doorbell. I've been told that it's and old telephone extension bell. I've attached a couple of pictures.

The back of the bell case has 40BPLU/3 printed on it

Is it possible to wire this (via a transformer?) to be used as a doorbell and if so what would I need?

I'm not too bothered if I can't use the bell as it stands as I will remove the actual bell and remount it on a piece of wood and get it to ring with parts from a modern bell.

Many thanks

 

[Spark123]

Might be better to look at plan B - if it is made for telecomms purposes then I doubt it will be 12v.

 

[Lectrician]

A telephone bell will be designed to ring on the 50v or more AC ring current of a telephone line. You cannot really use this as a door bell, even with an appropriate transformer - door bell contacts are not designed for this voltage.

You could use a relay, but this coupled with a transformer for the bell and a transformer or batteries for the relay is getting over engineered and expensive.

 

[Goldberg]

AC

 

[Lectrician]

YES! AC

A telephone line is DC when on hook and when dialling and setting up calls etc.

When a phone rings, AC is applied to the line rather than DC. This is what causes the phones to ring.

What do you think the capacitor is there for on a master socket? IT BLOCKS THE DC FROM REACHING THE AC BELL.

Don't shock horror me I aint in the mood. Go learn something.

 

[Goldberg]

When a phone rings, AC is applied to the line rather than DC.

I did not know that.

Go learn something.

No need - I have humility, which always trumps being a grouchy tw*t.

 

[BOC]

Thanks guys, looks like plan B then

 

[Johnmelad502]

Go learn something.

No need - I have humility, which always trumps being a grouchy tw*t.

 

[TicklyT]

That bell is a DC one. There's an interrupter spring on the armature just to the right of the lower coil, so you should be in luck.

It looks like they were designed for fire brigade call out systems, not telephony, although they probably had other uses.

According to the spec. the design operating current is between 35 and 50mA DC, using up to 18 (leclanche) cells, so that's about 25 - 30 Volts.

Taking into account the line resistance was up to 800 Ohms, and that, along with the bell coils, formed a potential divider, it may well work satisfactorily on a 9 or 12 Volt DC supply.

P.O. ENGINEERING DEPT.
ENGINEERING INSTRUCTIONS
MISCELLANEOUS
Fire Alarms
B 1010
Issue 1, 1938

2. Bells (battery operated)
The operating data indicated below are applicable when the bells are used for fire-alarm purposes only.

(a) “Bell No. 17C”. 500 ohms, 3in. gong; used indoors on omnibus call-bell systems when a moderate ring is required.

Operating Data
Nominal current 50mA
Minimum current 35Ma
Maximum No. of cells 18


(b) “Bells, Nos. 40A and 40B”. 50 + 50 ohms and 500 ohms, 4in, gongs; used indoors when a loud ring is required.

(i) “Bell No. 40A” with coils in parallel (25 ohms); is usually connected in the local alarm contacts of an indicator for continuously-ringing bell systems.

Operating Data
Nominal current Coils in Series 90mA Coils in parallel 170mA
Minimum current Coils in Series 70mA Coils in parallel 120Ma
Maximum No. of cells Coils in Series 6 Coils in parallel 3


(ii) “Bell, No. 40B”. 500 ohms; is specified for omnibus call-bell systems in indoor locations.
Operating data As for “Bell No. 17C.”

(c) ”Bell No. 41A“. 50 + 50 ohms, 3in. gong; used similarly to “Bell No. 40A,” when a moderate ring is required.
Operating data As per “Bell No. 40A.”

 

[Lectrician]

When a phone rings, AC is applied to the line rather than DC.

I did not know that.

Go learn something.

No need - I have humility, which always trumps being a grouchy tw*t.

Yea, ok.

Sorry about that. Had a very bad day. Some of us are entitled to be grouchy ****s at times.

 

[Goldberg]

I agree. Hope your day improves.

 

[TicklyT]

When a phone rings, AC is applied to the line rather than DC. This is what causes the phones to ring.

More fully, during ringing, pulses of AC (usually 75 Volts, 17 Hz in 2/7 time), are superimposed on the 50 Volts DC normally seen on the line.

IIRC the DC line polarity is reversed as well.

 

[ban-all-sheds]

I've attached a couple of pictures.

Are they very, very, very small?

 

[Chri5]

When a phone rings, AC is applied to the line rather than DC. This is what causes the phones to ring.

More fully, during ringing, pulses of AC (usually 75 Volts, 17 Hz in 2/7 time), are superimposed on the 50 Volts DC normally seen on the line.

IIRC the DC line polarity is reversed as well.

The BT instructors used to refer to it as alternating DC