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Old 22nd Sep 2008, 10:54 pm   #1
Darren-UK
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Default 706 Mk1 pushbutton wiring.

I've got an early 706 fitted with a 'Bell on/off' pushbutton. The telephone has already been converted for PST use but the three wires to the pushbutton (more precisely, the switch it operates) have been removed.

Does anyone know to which terminals the wires should be connected to? I also wondered if the disconnection was a necessary part of the PST conversion but I don't know.

According to here, the relevant GPO wiring diagram for the pushbutton part of the circuit is N809 but I can't download it due to format problems.
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Old 22nd Sep 2008, 11:50 pm   #2
trevwgb
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Default Re: 706 Mk1 pushbutton wiring.

Hi
Is this any good? Fig 3 ?
http://www.samhallas.co.uk/repositor.../0000/N806.pdf
Regards
Trev
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Old 23rd Sep 2008, 12:14 am   #3
Kat Manton
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Default Re: 706 Mk1 pushbutton wiring.

Hi Darren,

No problem using OS X here (well, apart from that document index totally missing the point of the Internet by being spreadsheet in a proprietary Microsoft format.)

The Excel spreadsheet (which opened with NeoOffice Calc) seems to be an index to back to documents also indexed here; the documents themselves being PDF.

Cheers, Kat
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Old 23rd Sep 2008, 12:27 am   #4
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Default Re: 706 Mk1 pushbutton wiring.

The switch was wired so that the bell was short-circuited when the switch was in the "OFF" position. Before the advent of the modern socket all telephone bells were wired in series with the capacitor. The wiring had to be such that at least one bell could not be short-circuited. This arrangement was known as a Plan 1A.

Modern sockets have the bells wire in parallel, so I assume the switch would have to be wired in series with the bell so as to disconnect it.
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Old 23rd Sep 2008, 12:38 am   #5
Darren-UK
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Default Re: 706 Mk1 pushbutton wiring.

Thanks Trev, Kat, Graham. It's that nutty spreadsheet thing I couldn't run, but the reasons for that are not relevant here.

I'd assumed N809 to be an actual wiring diagram, not details of the pushbutton itself . Oh well.

The page Trev linked to is that from Bob Freshwaters' site to which I linked in post #1. Fig 3 thereon shows the wiring for when switch 5A is used as a recall button. I need the wiring for when 5A is used as Bell on/off and that's the elusive one.

I guess I can experiment, with the 'normal' 706 Mk1 cct in front of me, to try and get it working and by taking onboard Grahams' comments.

Last edited by Darren-UK; 23rd Sep 2008 at 12:41 am. Reason: Edited to embrace Grahams' post.
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Old 23rd Sep 2008, 3:06 pm   #6
AndiiT
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Default Re: 706 Mk1 pushbutton wiring.

Hi,
The Switch 5A-3 is wired as follows - Slate (Grey) lead is the common contact, the Brown lead is normally closed and the Blue normally open. To wire the switch to act as a Bell on/off switch in a telephone converted for modern plug and socket working strap as follows -

Remove strap T16 - T17 and connect the Switch leads Slate and Brown to T16 and Blue to T17. If you find that the operation of the switch is reversed (i.e. the 'Off' position allows the bell to ring and vice versa) swap the Blue and Brown leads over. The unused lead could also be parked on an unused terminal (T11 to T14 as I recall) if you wish.

Regards
Andrew
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