GPO 746 Dial Removal and light Help please

[Lee Greenhithe]

Hi, all
Help needed please.Have a GPO 746 and wish to remove the dial and turn into an extension telephone (have a blank cover).is it just a case of removal of dial or do I need to change anything else.
Also need to add a 3.3 resistor,are these ones I can get off ebay.
Last one sorry,would like to add a red light to flash with bell, have a 220v bezel light (like car dash light) can I connect this and where please.(can get a lower voltage if needed )
Sorry if long winded
Thank You for your time, Lee

[julie_m]

You will need to short the pulse contacts (pink and orange), if you remove the dial.

A mains-rated neon indicator with series resistor will light with ringing if connected across the bell coils. You can reduce the resistor value to squeeze a bit more light out of it, but don't go below about 47 kΩ or you'll just blacken the inside of the glass. Or use a 110V-rated indicator.

[nutteronthebus]

Hi If you can get one there use to be a handset with a neon bulb built it

Dave

[nutteronthebus]

Hi a quick check and the is one on ebay at this time

[TonyDuell]

On the 746, the dial wiring harness (5 wires) is connected to the screw terminals
at the back edge of the PCB. To avoid having wires flapping about inside (and probabably shorting to things they shouldn't), you could remove this totally and connect a jumper wire between terminal T8 and terminal T10 (leaving the other wires on these terminals connected as they were). This will bypass the impulse contacts on the dial.

I do wonder why you are removing the dial, it was normal to leave it fitted on an extension telephone.

As for the handset with the neon, that's a Handset 7, diagram N1901 applies. Or Handset 17A which has the amplified earpiece of a Handset 14A. Diagram N1843 covers the Handset 17A. The original wiring of this, of course, put the neon in the series circut of bells, and you had to put a shunt resistor in parallel with the neon (or it did blacken). You can try wiring it as for a telephone with no extension bells (and leave out the 3k3 resistor you normally fit for coversion to the Plug 431A wiring), if it and all other telephones on your line ring OK then leave it like that.

[AndiiT]

Hi,
In my experience the neon handsets don't work too well when the phone is wired to the "new" (30+ years old now) plug and socket system (PST wiring).

As has previously been mentioned in the original N digram the neon was connected in parallel across a resistor in series with the bell, you can try doing this across the 3k3 resistor required between T4 and T5, in a modified phone but this may only work if the bell motor coils are 1k impedance and not 4k impedance where the resistor wouldn't be required anyway.

With PST wiring I find that the easiest way to get the neon in the handset to light is to exploit the unused 1.8Uf capacitor between T9 and T7 with a suitable series resistor, found by experiment but usually between 1k and 4k Ohms, in one of the leads of the neon.
So to clarify

PST wiring with neon handset

Straps

T8 - T9
T4 - T5 - T6 (if 4K bell)
3k3 resistor between T4 and T5 - T6 (if 1K bell)

T16 - T17- T18 - T19

Line cord

Red - T8
White - T18
Blue - T5
Green - T11 (would normally be parked on T15 but see handset wiring below)

Handset (with neon)

White - T10
Red - T1
Green - T2
Blue - T3
Black - T15
Orange - T7

Connect series resistor, value as mentioned earlier between T15 and T16

If you have no luck in finding a handset incorporating a neon just wire as above and connect your additional neon between T15 and T7


Regards

Andrew