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Old 30th Jan 2007, 6:55 pm   #1
Dave Moll
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Default 700 series telephone handset with neon

I have recently acquired this item, and I wonder whether anyone knows how the neon needs to be wired.

I have read the section in Bob Freshwater's site concerning handset 17a (the nearest I can find - mine does not have the volume control), which implies that I can wire then neon in series with the bell, with a resistor in parallel. What sort of value should I use?

Or would I have to install a lamp signalling unit to make it work?
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Old 30th Jan 2007, 9:36 pm   #2
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Default Re: 700 series telephone handset with neon

Hi,
You should not need a lamp signalling unit to get your handset to work, if the phone is already wired for "modern" plug and socket working try connecting the black of the handset lead to T4 and the Orange to T16 - This connects the neon in parallel across the bell coils and may work.

If the bell coils are 1k (usually two 500 ohm coils in series) ensure that there is a 3k3 resistor connected across T4 - T5 as per these instructions (which also advise of the correct strapping for PST working)

http://www.britishtelephones.com/pstconv1.htm#700

Alternatively try the following;

Strap T16 - 17 - 18 - 19 and connect White of line cord to T18

Green of line cord to T15 (spare)

Strap T6 - T5 and connect Blue of line cord to T6

Connect Orange from handset to T5 and Black from Handset to T4

Fit 15k (or 100k) resistor across T5 - T4

Remove Strap T7 - T6 and connect Red of line cord to T8
(you may also remove strap T8 - T9 If fitted although this is optional and should not affect operation)

NOTE - You may have to experiment with the value of the resistor across T5 - T4 and if ringing problems are experienced (1k bell coils) substitute Strap T16 - T17 with a 3k3 resistor if using the alternative suggested method

The following link shows wiring of the Lamp signalling handset, it is the top right hand diagram that should be useful

http://www.samhallas.co.uk/repositor...1000/N1901.pdf

Remember when the lamp signalling handset was introduced bell circuits were wired in series, unlike today where they are parallel wired, which is what can cause some confusion.

Happy wiring

Andrew
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Old 31st Jan 2007, 12:20 pm   #3
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Default Re: 700 series telephone handset with neon

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Originally Posted by AndiiT View Post
if the phone is already wired for "modern" plug and socket working try connecting the black of the handset lead to T4 and the Orange to T16 - This connects the neon in parallel across the bell coils and may work.

If the bell coils are 1k (usually two 500 ohm coils in series) ensure that there is a 3k3 resistor connected across T4 - T5 as per these instructions (which also advise of the correct strapping for PST working)
The 'phone was already wired for PST as per Bob Freshwater's instructions, including the 3k3 resistor between T4 and T5, and one of the combinations I had already tried was with the neon in parallel with the bells (albeit with the leads reversed). I have now tried the wiring suggested above, but with no joy.

The thought occurs that perhaps I should check out the neon by powering it up directly (say using a variac and series resistor). If the neon simply doesn't work, I could waste a lot of time trying different configurations. I will try that and let you know how I get on.

Thanks for the pointer to the wiring diagram. I had tried to find it and failed.
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Last edited by Dave Moll; 31st Jan 2007 at 12:24 pm. Reason: added note about wiring diagram
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Old 31st Jan 2007, 6:44 pm   #4
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Default Re: 700 series telephone handset with neon

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The thought occurs that perhaps I should check out the neon by powering it up directly (say using a variac and series resistor).
Actually, I decided to use a telephone magneto (connected using a BT master socket) instead. The neon flashes nicely, even with a 100k resistor in series - connected to the ringer output of the socket. I hasten to add that the BT socket is only connected to the magneto, not the telephone network!

I then tried the neon in the 'phone (which I plugged into the magneto output), first in parallel with the bell, then in parallel with "that resistor". Yes, it flashes (rather feebly), but the sound of the bell (which is very feeble on the set I'm using) indicates that the ringer circuit is being driven harder by the magneto than BT's ringing current drives it.
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Old 31st Jan 2007, 10:46 pm   #5
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Default Re: 700 series telephone handset with neon

Quote:
Originally Posted by Dave Moll View Post
The 'phone was already wired for PST as per Bob Freshwater's instructions, including the 3k3 resistor between T4 and T5, and one of the combinations I had already tried was with the neon in parallel with the bells (albeit with the leads reversed).
The Black and orange leads are connected directly to the neon so the "polarity" of them is not important.

I had a 746 some time ago with a neon signalling handset and has some problems getting the neon to light on incoming ringing. I am sure that I eventually succeeded though - I will have a dig about tomorrow (day off) and see if I still have the phone kicking around and check how it is wired.

Andrew
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Old 31st Jan 2007, 10:53 pm   #6
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Default Re: 700 series telephone handset with neon

Hi again,
Having given this a bit more thought, you could "cheat" and exploit the ringing capacitor in the phone (if this is fitted) to drive the neon independently of the bell, connect strap T8 - T9 (if not already fitted) and connect the neon orange to T7 (ensuring that there are no other connections to T7) and the neon black to T16; it might not hurt to experiment with a series resistor connected between the neon black lead and T16 (suggest using T14 - T16 as anchor points for the resistor and, of course in this case, connecting the neon black lead to T14)

Andrew
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Old 1st Feb 2007, 12:08 am   #7
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Default Re: 700 series telephone handset with neon

Brilliant! Many thanks for that. Problem now solved.

Yes, those spare terminals do come in useful from time to time. This time a resistor. Elsewhere I have used them for a bell-silencing switch.
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Old 12th Feb 2007, 10:29 pm   #8
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Default Re: 700 series telephone handset with neon

Hi It just so happens somebody else wanted to know how to connect the extra wires on a 700 handset with neon.I dug out one of my old diagrams and found the correct way of wiring it.The black wire goes to terminal 4 and the orange wire goes to terminal 5.Between terminals 4 and 5 you need to put a carbon resistor with a value of 15000 ohms.If you have an old 700 phone (pre white plug in type) with 1000 ohm bell coils then this resistor will do both jobs.You will not need two resistors ,so if you have fitted a 3.3k resistor between 4 and 5 replace it with the 1500 ohm one.
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Old 12th Feb 2007, 11:21 pm   #9
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Default Re: 700 series telephone handset with neon

Nigel, could you please clarify two points:
1) Should the value be 1500Ω or 15000Ω? I imagine the latter.
2) Am I right in thinking that the neon and resistor are in parallel between T4 and T5?

Incidentally, I believe that one of the options I tried was in parallel with the resistor and in series with the bell. As I recall, I could not get the neon to light in this configuration, even with the resistor value increased above 15KΩ (which merely stopped the bells from getting sufficient current to ring properly).
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Old 13th Feb 2007, 12:15 am   #10
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Default Re: 700 series telephone handset with neon

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Originally Posted by Dave Moll View Post
Should the value be 1500Ω or 15000Ω? I imagine the latter.
I imagine the former, but I am only a dentist rather than a phone engineer, so I'd wait to see what the experts say
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Old 13th Feb 2007, 10:56 am   #11
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Default Re: 700 series telephone handset with neon

Hi,
In the original 700 series telephones any additional signaling device such as an external bell, or in this case a neon indicator was wired in series with the 1K ohm (normally two 500 ohm coils in series) bell coils.
As a neon indicator is not a resistive device (as I am sure we all know) a medium value resistor was wired in series with the bell coils and the current developed across it during ringing was used to light the neon.

With the advent of the PST (Plug, socket and telephone system) in around 1982, the bell circuit became a parallel wired design, the bell coils being increased in impedance to 4k Ohms, which enabled a maximum of 4 bells/calling devices to be connected across the line, I seem to recall mentioning this either in this thread or elsewhere in the forums.
In practice it depended on how near or far away from the exchange you were, some subscribers could get five phones on the line with no problems others struggled with three.

As the original "hard wired" design is for series working this may explain some of the problems that Dave Moll had trying to get the neon to light, similar to problems I had in the past when trying to get a lamp signaling handset to operate on a present day system.

Although the method I described further back in this thread (i.e. using the original bell capacitor in the phone to drive the neon) is not the desired way of wiring, I suspect that it may be one of the only ways to get a lamp signaling handset to operate these days - If you are worried about BT finding too higher capacitor 'kick' when they do their automated line testing I can suggest ways of preventing this (you can always PM me if you are curious) but are a little OT for this discussion.

Andrew
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