746 Conversion Help - UK Vintage Radio Repair and Restoration Discussion Forum

ngilbo67 · 2nd Sep 2016, 1:55 pm

Hi - just converting what I believe to be a 746. Have a conversion kit but have some additional wires I can't find in any wiring diagram. The wires are blue, brown and grey and are coming from just under the phone button (or so it appears). Anyone provide into insight as to where these needs to be located? I've attached an image which will hopefully help.h

Thanks
Nick

AC/HL · 2nd Sep 2016, 2:10 pm

Hello Nick & welcome.
Those wires are for the auxiliary switch. What does the button say?
If you don't want to use them, they can be parked on one of the spare contacts (11-14)

TonyDuell · 2nd Sep 2016, 2:18 pm

As Bill said, those are from the pushbutton switch. This is a changeover switch, so 3 wires (common, normally open, normally closed). I forget the colour code, but I can look it up if you need it.

As it is currently wired, 2 of them go to one side of the line (T19), the other goes to T11 which is just a spare terminal, not connected to anything on the PCB. The telephone should work like this, but the button will not do anything. If you are happy with that, you can leave it all alone.

Dave Moll · 2nd Sep 2016, 2:40 pm

Is the switch latching (i.e. toggles between one state and the other) or momentary (changes state while pressed but returns when released)? This can be checked using a multimeter between switch's spade terminals.

If it's the former, it could be wired as a bell on/off switch if you wish, if the latter it would only really be useful on a private exchange that uses "earth recall" for any special functions such as call transfer.

ngilbo67 · 2nd Sep 2016, 3:09 pm

Thanks for the reply everyone - great forum!

I followed these instructions and everything seems to work (not sure what the button is for though

)...

Bell On/Off switch
To fit a bell on/off switch obtain and fit the following items:-
(746 style phones need 2 pins, On/Off button and Switch No. 23A, whilst 706 phones need Switch No. 5A and the appropriate coloured On/Off button).

Wire and install as follows:-

Remove strap T16 - T17 only. Leave T17-T18 and T19 in place with the white of the line cord.
Connect Brown wire of switch to T16.
Connect Grey and Blue wires of the switch to T17.

Dave Moll · 2nd Sep 2016, 7:25 pm

Quote:

Originally Posted by ngilbo67

not sure what the button is for though

"Bell on/off" does pretty much what it says. In one state the bell will ring on an incoming call, in the other it will remain silent. The latter could be useful if you want to avoid being disturbed by incoming calls that are nine times out of ten direct marketers.

keithinuk · 4th Sep 2016, 9:19 pm

The one I got today seems to have most of the extras, two switches, Main and Two, I suspect you could convert to one to a mute, I don't know about the other one.

TonyDuell · 4th Sep 2016, 9:31 pm

That's the first extension for Plan 105. The main telephone was a Planset (diagram N625), there were 2 extensions, one with buttons 'main' and '2' , the other with 'main' and '1'. The extensions could call the main set, could be called by the main set, and could call each other. Normally incoming calls would ring the bell at the main telephone (typically used by a secretary) who could transfer them to the appropriate extension.

Diagram N4507 shows the wiring and operation for Plan 105

The thing on the side of the handset cradle that looks like a buzzer is a buzzer, operating off about 12V DC. It is operated when the main telephone or the other extension calls this one.

I hate to say this, but I find it a great pity when such telephones are simply converted back to a normal, single-line 746. I would rather use them with a Planset.

Nickthedentist · 5th Sep 2016, 8:46 am

OTOH, they can always be converted back, I suppose.

keithinuk · 5th Sep 2016, 8:59 am

I still have the original 9 wire lead and junction box, but its not really usable at home.

TonyDuell · 5th Sep 2016, 2:19 pm

Well, yes, they can be converted back if you still have the right parts (2 switches + plungers, the right 2 buttons + pins, the buzzer, the 9 way line cord and the right block terminal). But then any 746 can be converted if you have the right parts. That's how they were made in the first place, I am told the necessary bits were assembled at the subscribers site in many cases.

Point is that 746s are relatively common. The buzzers and switches are much less so.

I guess I am more interested in the electronics side, which is why I find these odd telephones fascinating. Personally, I'd keep the Plan 105 extension as it is. Get another 746 (as I said they are not exactly rare!) if you want a normal telephone. Get a Planset (not common, but they do exist) and wire up Plan 105 or Plan 107. 8 D cells will do to power it.

AC/HL · 5th Sep 2016, 2:49 pm

Can you answer a call from the extensions, or would you need to run to the plan set?

TonyDuell · 5th Sep 2016, 5:25 pm

I believe you have to have the 'EXTN to EXCH' key down on the Planset for this. You could
leave this down, and either answer at the extension or release the key (at the Planset) and answer there.

Dave Moll · 5th Sep 2016, 9:38 pm

Quote:

Originally Posted by TonyDuell

8 D cells will do to power it.

That may be overkill. I run mine (albeit with a single extension) successfully from one PP9 battery, although I believe the specified operating voltage is 10V.

TonyDuell · 6th Sep 2016, 1:45 pm

The official supply if no mains was available was 8 Flag cells in a battery box. 8 Alkaline D cells have about 1/3-1/2 the capacity (on paper) and thus should last a long time. A 9V PP9 will work, the actual current the Planset draws is not that great, but will not last as long.

2nd Sep 2016, 1:55 pm	#1
ngilbo67 Retired Dormant Member Join Date: Sep 2016 Location: Neath, Neath Port Talbot, Wales, UK. Posts: 2	746 Conversion Help Hi - just converting what I believe to be a 746. Have a conversion kit but have some additional wires I can't find in any wiring diagram. The wires are blue, brown and grey and are coming from just under the phone button (or so it appears). Anyone provide into insight as to where these needs to be located? I've attached an image which will hopefully help.h Thanks Nick Attached Thumbnails

2nd Sep 2016, 2:10 pm	#2
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: 746 Conversion Help Hello Nick & welcome. Those wires are for the auxiliary switch. What does the button say? If you don't want to use them, they can be parked on one of the spare contacts (11-14)

2nd Sep 2016, 2:18 pm	#3
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: 746 Conversion Help As Bill said, those are from the pushbutton switch. This is a changeover switch, so 3 wires (common, normally open, normally closed). I forget the colour code, but I can look it up if you need it. As it is currently wired, 2 of them go to one side of the line (T19), the other goes to T11 which is just a spare terminal, not connected to anything on the PCB. The telephone should work like this, but the button will not do anything. If you are happy with that, you can leave it all alone.

2nd Sep 2016, 2:40 pm	#4
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,127	Re: 746 Conversion Help Is the switch latching (i.e. toggles between one state and the other) or momentary (changes state while pressed but returns when released)? This can be checked using a multimeter between switch's spade terminals. If it's the former, it could be wired as a bell on/off switch if you wish, if the latter it would only really be useful on a private exchange that uses "earth recall" for any special functions such as call transfer. __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

2nd Sep 2016, 3:09 pm	#5
ngilbo67 Retired Dormant Member Join Date: Sep 2016 Location: Neath, Neath Port Talbot, Wales, UK. Posts: 2	Re: 746 Conversion Help Thanks for the reply everyone - great forum! I followed these instructions and everything seems to work (not sure what the button is for though )... Bell On/Off switch To fit a bell on/off switch obtain and fit the following items:- (746 style phones need 2 pins, On/Off button and Switch No. 23A, whilst 706 phones need Switch No. 5A and the appropriate coloured On/Off button). Wire and install as follows:- Remove strap T16 - T17 only. Leave T17-T18 and T19 in place with the white of the line cord. Connect Brown wire of switch to T16. Connect Grey and Blue wires of the switch to T17.

4th Sep 2016, 9:19 pm	#7
keithinuk Retired Dormant Member Join Date: Mar 2011 Location: Hertfordshire, UK. Posts: 208	Re: 746 Conversion Help The one I got today seems to have most of the extras, two switches, Main and Two, I suspect you could convert to one to a mute, I don't know about the other one. Attached Thumbnails

4th Sep 2016, 9:31 pm	#8
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: 746 Conversion Help That's the first extension for Plan 105. The main telephone was a Planset (diagram N625), there were 2 extensions, one with buttons 'main' and '2' , the other with 'main' and '1'. The extensions could call the main set, could be called by the main set, and could call each other. Normally incoming calls would ring the bell at the main telephone (typically used by a secretary) who could transfer them to the appropriate extension. Diagram N4507 shows the wiring and operation for Plan 105 The thing on the side of the handset cradle that looks like a buzzer is a buzzer, operating off about 12V DC. It is operated when the main telephone or the other extension calls this one. I hate to say this, but I find it a great pity when such telephones are simply converted back to a normal, single-line 746. I would rather use them with a Planset.

5th Sep 2016, 8:46 am	#9
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,846	Re: 746 Conversion Help OTOH, they can always be converted back, I suppose.

5th Sep 2016, 8:59 am	#10
keithinuk Retired Dormant Member Join Date: Mar 2011 Location: Hertfordshire, UK. Posts: 208	Re: 746 Conversion Help I still have the original 9 wire lead and junction box, but its not really usable at home.

5th Sep 2016, 2:19 pm	#11
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: 746 Conversion Help Well, yes, they can be converted back if you still have the right parts (2 switches + plungers, the right 2 buttons + pins, the buzzer, the 9 way line cord and the right block terminal). But then any 746 can be converted if you have the right parts. That's how they were made in the first place, I am told the necessary bits were assembled at the subscribers site in many cases. Point is that 746s are relatively common. The buzzers and switches are much less so. I guess I am more interested in the electronics side, which is why I find these odd telephones fascinating. Personally, I'd keep the Plan 105 extension as it is. Get another 746 (as I said they are not exactly rare!) if you want a normal telephone. Get a Planset (not common, but they do exist) and wire up Plan 105 or Plan 107. 8 D cells will do to power it.

5th Sep 2016, 2:49 pm	#12
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: 746 Conversion Help Can you answer a call from the extensions, or would you need to run to the plan set?

5th Sep 2016, 5:25 pm	#13
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: 746 Conversion Help I believe you have to have the 'EXTN to EXCH' key down on the Planset for this. You could leave this down, and either answer at the extension or release the key (at the Planset) and answer there.

6th Sep 2016, 1:45 pm	#15
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: 746 Conversion Help The official supply if no mains was available was 8 Flag cells in a battery box. 8 Alkaline D cells have about 1/3-1/2 the capacity (on paper) and thus should last a long time. A 9V PP9 will work, the actual current the Planset draws is not that great, but will not last as long.