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Old 29th Nov 2017, 8:07 pm   #1
CurlyCord
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Default GPO 706/746 Ringer on/off Button

Hi guys, I have a couple of old 700 series telephones from the 60's & 70's can anyone tell me what terminals the ringer on/off button needs to be connected to?
The phones have been converted with modern BT style leads and the links have been moved accordingly. I'm guessing the 3 wires need to be moved to other terminals as the buttons don't currently work?

Thanks
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Old 29th Nov 2017, 9:00 pm   #2
TonyDuell
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Default Re: GPO 706/746 Ringer on/off Button

The original GPO wiring put multiple bells in series. The bell on/off switches short-circuited a bell in the off position. The BT wiring puts multiple bells in parallel, so the switch needs to open that bell circuit when the bell it turned off.

The switch has 3 wires as you noted, it is a changeover contact. With your multimeter identify the 2 wires that are connected when the switch is in the 'on' position. Either insulate the other wire with tape (that was an official thing to do!) or park it on a spare terminal. Terminals T11 to T15 are normally spares (not wired to anything else inside the telephone) but one is probably used to park the green wire of the line cord.

Remove the strap between termianls T16 and T17 (notice that one of the bell wires is connected to T16, leave that there) and connect the remaining 2 swtich wires to T16 and T17 (either way round). This puts the switch in series with the bell so you can open the bell circuit to turn the bell off. Leave the other strap from T17 (to T18) in place of course.
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Old 29th Nov 2017, 10:18 pm   #3
Oldcodger
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Default Re: GPO 706/746 Ringer on/off Button

From dim & distance memory of fitting Plan1A, where bells were in series, the button was marked on/off and using the switch in reverse will show the bell on, when in fact it's off. (Unless my memory is playing tricks as it's about 47 years since I last was on subs app fitting)
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Old 30th Nov 2017, 6:04 am   #4
TonyDuell
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Default Re: GPO 706/746 Ringer on/off Button

Fortunately (as I said) these switches have a changeover contact so you can wire them to to be closed in whichever position you want.
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Old 30th Nov 2017, 5:40 pm   #5
OscarFoxtrot
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Default Re: GPO 706/746 Ringer on/off Button

Quote:
Originally Posted by Oldcodger View Post
From dim & distance memory of fitting Plan1A, where bells were in series, the button was marked on/off and using the switch in reverse will show the bell on, when in fact it's off.
Indeed.

I wired the second pole of a 746 bell off switch in series with pin 2 of the line cord, so when the bell was on the phone was off and vv. in other words, to answer a ringing call the bell off switch had to be operated.

Foxed my mother who tried answering a call on my phone, found it carried on ringing, and had to run to another room.

I suppose the computer equivalent is reversing people's mouse buttons left-right.
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Old 2nd Dec 2017, 1:12 pm   #6
CurlyCord
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Default Re: GPO 706/746 Ringer on/off Button

Hi Tony, I wired the switch as you suggested. The phone will only ring now when the button is held down. What am I missing?
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Old 2nd Dec 2017, 2:28 pm   #7
Dave Moll
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Default Re: GPO 706/746 Ringer on/off Button

It sounds as though you have a non-latching switch, as used for "recall" on a PBX or "call exchange" on a shared service (party line), rather than the latching type required for bell on/off.
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Old 2nd Dec 2017, 4:52 pm   #8
CurlyCord
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Default Re: GPO 706/746 Ringer on/off Button

Hi Dave, yes looking at it I think it is a recall type button rather than a bell on/off button.

Many thanks for your help.
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Old 3rd Dec 2017, 10:21 pm   #9
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Default Re: GPO 706/746 Ringer on/off Button

I thought I would contribute this anecdote of the bell switch on my parents bedroom extension in my childhood home, and ask if it was a common scenario.

The phones were GPO 332, and had a single button for earth-leg recall.

The bell switch was a porcelain & bakelite tumbler switch mounted in the skirting board and wired into the bakelite junction-box so as to short the local bell when the switch was closed. It was a normal one way mains light switch with ON OFF marked on the bakelite cover, but as the body of the switch was mounted upside-down on the wall, the switch was closed when it was in the OFF position.

Eventually a engineer called to replace the 332s with 706s, we still had the party-line but I can't remember if the skirting board switch was still connected or just abandoned, as I suppose its purpose was to stop me and my sister from being woken up as babies

I was hoping the engineer would forget to take the old pones with him, but I was out of luck.
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