706 Conversion

[doooford]

Hello all, I'm new here but this forum looks like just what I need!
I'm often starting projects in restoring old kit, but it's been on the back burner recently as 2 years ago we had a son who has meant all of my side projects have been on the back burner!
So, last night I found a 706L that I started converting 2 years a go or so for a friend, luckily they don't mind how long it takes, I'd be in a rage if it was me after 2 years
Unfortunately, I was half way through doing it before it got put in the cupboard and I can't find the instructions that I was using! This post https://www.vintage-radio.net/forum/...ad.php?t=61308 is what I'm going to compare my work with tonight but it may be that I get stuck and have to take some pictures and report back here tomorrow.
This is just a polite request for help really and a warning that I may be back. I didn't want to look like one of those newbies that comes on to a forum for help and then dissappears.
All may go to plan, I'll let you know

[Darren-UK]

This is the site most of us refer to and is probably the source of the info in the other thread.

You should be able to convert a 706 in ten minutes, providing you have the required resistor to hand and don't need to change the carbon granule receiver (handset, if you prefer) inserts.

[doooford]

Thanks Darren. Bang on. That was the instruction list that I had. Many thanks

[doooford]

Hi all. Almost done on the conversion. 2 things I'm stuck on now though!
The phone only has White, Green and Red wires so haven't been able to connect the blue wire to T6 for obvious reasons.
Secondly, the owner of the phone supplied a plug and cable to connect to and a chocolate block. The cable has Yellow, Red, Green and black wires I'm going to snoop around the forum and see what I can find about this link but any help would be appreciated

[doooford]

I'm assuming that I have a non uk cable so can link like this? http://www.britishtelephones.com/pstconv2.htm

So now I'm just confused as to where my missing blue wire is?

[Dave Moll]

Although there do seem to be variations, on your Y/R/G/Bk lead the equivalance to a normal lead is possibly:

yellow = red
red = green
green = blue
black = white

I have a number of leads using this convention.

By the way, when using an old-fashioned R/G/B lead I tend to use the green wire to stand in for the blue, given that green in a modern four-wire lead is not usually needed.

[doooford]

Thanks Dave. I'll look at this tomorrow as this colour mixing is mashing with my head. What harm can a bit of trial and error do?

[Darren-UK]

Attached is a little diagram I refer to from time to time, which you may find handy for cross-referencing wiring colours.

The diagram was borrowed from one or other website a long time ago, the URL of which escapes me now.

Note that, assuming a D section linecord, the diagram will assume the flat side of the cord is at the underside.

[doooford]

Originally Posted by Darren-UK

Attached is a little diagram I refer to from time to time, which you may find handy for cross-referencing wiring colours.

The diagram was borrowed from one or other website a long time ago, the URL of which escapes me now.

Note that, assuming a D section linecord, the diagram will assume the flat side of the cord is at the underside.

Fantatic advice Dave and Darren-UK. I still don't quite understand why there is no blue wire but will see what effect this has.

So I'll be trying this:-

yellow = red
red = green
green = Nothing
black = white

[Dave Moll]

I'm not sure that's quite right. For three-wire operation (i.e. using the ringer capacitor in the master socket) you need the blue (i.e. green in the Y/R/G/Bk convention) connection, so green in the plugged cord going to green in the old lead, but this is connected at the instrument end as though it were a blue wire. It is the red in the plugged lead which is not needed. Somewhat confusing, but I hope this makes sense.

[AndiiT]

Originally Posted by doooford

The phone only has White, Green and Red wires so haven't been able to connect the blue wire to T6 for obvious reasons.

Originally Posted by doooford

So now I'm just confused as to where my missing blue wire is?

Hi,
Some early 706 phones were fitted with a 3 wire cord and a block terminal (BT)30A, later models had a four -wire line cord and a BT52A; If this is the original phone line cord i.e. the "hard wired" one, the green lead would have originally been spare and the link in the Block terminal which would have originally maintained the bell circuit across the green and white wires on a four - wire cord would have been fitted across T17 - T18 in the telephone itself.

I would proceed as Dave suggests and treat the Green wire as the missing Blue.

Strap the phone as follows -

Remove T4 - T5 and replace with a 3k3 resistor (not important if you don't have a resistor to hand just leave the strap in place)

Strap T5 - T6
Strap T16 - T17 - T18 - T19
RED of line cord to T8 (ensuring that Orange of dial cord also goes to this terminal if not wired via the PCB)
WHITE of line cord to T18
GREEN of line cord to T6

Connect the three wires of your line cord to the Block terminal, then from what I can see of your previous posts connect the plug ended cord as follows -

Yellow to red
Black to White
Green to Green

If you then are able to get dial tone and make outgoing calls but you have no ringing on incoming calls try swapping the Yellow (Red) and Black (White) leads over.

Regards
Andrew

[doooford]

Hi Andrew,

I followed your wisdom last night and plugged the phone in and...

Could dial in and out but no ringer. Then I remembered your advise on this. I got side tracked last night, but tonight I'll swap the wires over and we may then be in business on this. Thank you everyone for your help.

No surprises, but I have now had someone else ask if I can do their phone. It's a much older one but haven't been able to check what it is yet. Looks like a 70's phone on first glance.

Thanks again all

[Tim]

Hi
Don't worry about the blue wire (or abcence of)connected to terminal 6 in your phone. All you need are 3 wires(red,white and green). The blue wire connects to pin 4 in the phone socket but was only used for the recall button on switchboadrs and the like so isn't required for a 706/746 on a standard domestic line.

[doooford]

The results are in...

...Initially followed the instructions to the letter including 3k3r resistor. Could make and receive calls but no ringer.
So swapped white and red wires and...

...nothing I'm afraid. Well the same, it worked but ringer didn't. I then moved the green wire to T15, still the same.

I haven't fitted a rectifier, would that make a difference?

I'm at a loss and was hoping to return this tomorrow for a birthday present (bit tight I know as it should have been returned months/years a go).

Does anyone have any ideas? I have a multimeter so can do any tests necessary.

Many thanks

[AndiiT]

Hi,
Moving the Green wire to T15 will have no effect as terminals T11 - T15 are spare ones and don't connect anywhere.

As a temporary measure, leaving all other straps (and resistor) in place, strap T6 - T7 and T8 - T9 if the phone does not ring with these straps in place it's likely that the bell motor coils are open circuit, you can always check this with a multimeter switched to the K ohms range and look for around 1K ohm across the bell coils, these are, or should be wired direct to T6 and T16 respectively.

On the other hand if the phone does ring with the extra straps in place the ringing current is not being developed across the ringer wire on T6 (Via the resistor and straps T5 - T4) and the white wire on T18 (via straps T16 - T17 - T18)

The rectifier is only there to prevent acoustic shock in the earpiece.

Any chance of a picture of the internal wiring of the phone and your line cord as this may yield some clues.

Let us know how you get on.

Andrew

[doooford]

Thanks Andrew. I've bought the little gem into work with me today so will try those things later. I'll see if I can get a picture from my phone onto my "locked down" PC to get on here. Should be no problem. Would love it if you could spot a school boy error and then we could get it fixed today.
Just out of interest, if the coils needed replacing, is it possible to buy them anymore and if so at what price?

[AndiiT]

Hi,
Your best bet for replacement bell motor coils is another phone, there is a chap on eBay who sells loads of spares though, and he occasionally has bell coils.

Pictures would be great as we can then see what's going on.

Andrew

[doooford]

Hi Andrew. Please take a look at the wiring. Apologies for the quality but had to take it on a mobile as it's all I have at work!

Let me know what you think, or if you need any clarification on anything.

Thanks

[SeanStevens]

I might have a spare coil if you want to come to Bath to collect it.....

SEAN

[doooford]

Hi Sean, funnily enough I'm working in Bath this week. I'll just let Andrew check my wiring for glaring errors and if he thinks I've done good then I may need to come to a deal with you!
Thanks.