Won a Brit 706

[Stephen Furley]

I can tell you how to wire it up, but I'm going out now, I'll get back to you this evening.  I need to ask you a couple of questions.  What is the impedance of the ringer coils?  There are normally two coils, marked either 500 or 2000, and they are connected in series, for a total impedance of 1k or 4k Ohms.  Can you confirm that the cord on the left, when looking at the back of the 'phone, is the handset cord?  It looks that way, but in this country they are normally the other way round, so that the wires cross over inside; I don't know why, obviously it will make no difference to the way it works.  I'll check the positions of the straps in your picture when I get back.

It's based on the 706 Mk.1, but there are some differences, yours has that fixed circuit board in place of the smaller plug-in regulator board that ours have; what components are on it?

A couple of things which may be of interest; that thin metal thing attached to the left side of the main frame (when looking from the front) is to hold the hook switch down while working on the 'phone with the cover off.  I only discovered it recently, or rather I knew it was there, but only recently worked out what it is for.  If you hold the switch down, and then press the bottom end of this thing in, the top end will come outwards, and hook over the switch lever to hold it down.  I discovered even more recently, in the Post Office notes for installers of the Compact Telephone, that it's called a 'Lineman's latch', which is a bit odd because that sounds more like an American term.

On the same side, close to the bottom of the switch frame, there is a small square 'lump' on the plastic base, with four holes in it.  This seems to serve no purpose on your one, because all of the holes are empty.  On the G.P.O. model one of these holes had a small terminal fitted into it.  On CB (dial-less) models the wiring loom for a dial was still fitted, to facilitate later fitting of a dial if required.  The small spades on three of the wires were pushed into three of these holes, and the other two, for the pulse contact, were joined on the terminal.  Later, the CB model was no longer stocked, and if one was required a standard model would have the dial replaced by a blank, and the wires stored in these holes.  The Mk.2 version did not have these holes, and had to have a small terminal strip fitted which was not included as standard; this was the reason that I chose a Mk.1 as the basis for my dial-less 706 conversion.  G.P.O. N-Diagram N808 explains:

http://www.samhallas.co.uk/repository/n_diagrams/0000/N808.pdf

[McHeath]

Yes, the cord on the left is the handset cord.  The ringer coils are 500s.  That little metal hook on the inside is pretty neat, very handy when troubleshooting a phone.  Many a time on a 500 I simply lay the handset in such a way as it holds the hook switches down, but this is a much better idea. 

The actual hookswitch mechanism itself is simply a little black box with a press button, none of the elaborate switches that 500s have or that older British 700 series phones have.  I've seen such cheap little switches on late model non WE phone clones here in the US, like a Radio Shack 2554 from 1989 that I have.

[Stephen Furley]

Yes, the cord on the left is the handset cord.  The ringer coils are 500s.  That little metal hook on the inside is pretty neat, very handy when troubleshooting a phone.  Many a time on a 500 I simply lay the handset in such a way as it holds the hook switches down, but this is a much better idea. 

The actual hookswitch mechanism itself is simply a little black box with a press button, none of the elaborate switches that 500s have or that older British 700 series phones have.  I've seen such cheap little switches on late model non WE phone clones here in the US, like a Radio Shack 2554 from 1989 that I have.

This sounds like the switch fitted to the 746; I suspect that this model was still being used in Israel after it had been replaced by the 746 here.

It's wired up almost the same as ours were in the old days before the new-style sockets, when we had low-impedance ringers, with extension ones wired in series.  I can't see any numbers on your terminals, but if you number the top row 1-9 left to right when looking at them from the back, and the bottom row 10-19, again left to right then the 'A' wire (tip) normally goes to 18; in your case this seems to be the green wire.  It's actually going to 19, but since these two terminals are strapped it makes no difference.  The 'B' wire (ring) normally goes to 8, as the white wire does in your case.  The wire going to 17, red in your case, you shouldn't need to connect to anything on a normal 2-wire line since there is a strap between 17 and 18 on your 'phone.  This wasn't on our ones, but there was a similar link between these two wires in the connection box at the other end of the line cord.  The strap between 14 and 15 is also not on our 'phones, but 14 is normally an unused terminal, and 15 is used for the earth wire when earth recall is used with a PABX, so I suspect that this is just a spare link.  However, I would expect to find 16 strapped to 17; If the 'phone doesn't ring, move the spare strap to this position.

There are a couple of modifications that you might want to make.  I don't know what the impedance of a standard American ringer is, but when we changed to connecting bells in parallel we changed to 4k Ohm ones, If this in used as the only 'phone on a line then it should be ok, but if there are others, particularly if they are modern types, then the bell in this one may well draw too much current, and prevent the others from ringing properly; in this case remove the strap between terminals 4 and 5, and connect a 1k or 3.3k resistor in its place.  Take care not to lose the strap you remove, put it on spare terminals, 11, 12, 13 and 14, or between other terminals where there is already another strap fitted.

The other modification you might want to make is to add a component which was included in the 746, and was fitted to 706s when overhauled.  This was known by the GPO as a 'Rectifier element number 205', and its purpose is to prevent acoustic shock from loud noises in the earpiece, mainly when the hook switch is operated.  I believe a similar device is fitted to some American 'phones.  A similar component is very easy to make.  Take two small diodes, and place them side  by side, opposite ways round.  Twist the two leads together at each end, and bend them 90 degrees, far enough out from the ends of the diodes that the spacing between them is equal to the spacing between two terminals in the telephone.  Take two spades to fit the terminals, cut the leads of the diodes to a suitable length and solder them into the spades.  Bend the spades so that the diode leads are sticking up at about 45 degrees and attach between between terminals 1 and 2, i.e. in parallel with the receiver.  I would recommend making this modification.

If you want to fit a bell on/off switch there was somebody selling the appropriate switch and button on Ebay, I think he still has them, he did a week or so ago.  If you want to do this let me know, and I can point you to the right item, and tell you how to connect it.

You still have the problem of how to connect the 'phone to the line.  The best way would probably be to keep the existing plug, and use an old type Israel to US adapter, but I can't seem to find one listed anywhere; the other way round are easy to obtain.  You will probably want to keep the existing line cord, as a new American one would not have the square grommet to fit into the 'phone that the old one has.  Can the Israeli plug be opened, or is it sealed?  If it can be opened then the beast solution might be to fit an old-style 4-prong plug, and then a 4-prong to modular adaptor, if needed.  The 4-prong plug would also look right on a 'phone of this vintage.

[McHeath]

I will give all this a whirl.  How do you get the fingerhole dial ring off?

[McHeath]

Really took it apart tonight to clean it.  It's a bit more complex than the WE phones I'm used to working on, but finally got all the various thingies undone and unconnected and undoubtably mislaid.  Washing the housing and plastics, they are in very good shape and have little fading.  Have not yet tested it to see if it works with the US phone system as it is wired, figure I will do that after cleaning.

We like to watch British murder mysteries in our evenings, so we often see 700 series phones of some sort.  The other night we were watching a Midsomer Murder and the Doomed Woman tried to use a green rotary 706 but her evil killer husband had cut the wires!

[McHeath]

Well I cleaned it up and it looks great!  Threw the plastics in the dishwasher, then used rubbing compound and wax and it came out fine.   

When I hooked it up it actually worked.  Dials out, sound is okay, surprising.  It even rings, which really surprised me, did not expect that.  The Israeli plug comes apart and there were simple spade connections on the ends of the wires, I've put a picture up of it. 

The missus really really likes it, so I think it's going to be landing on her desk.

[bingster]

I really like the subtly different shades of yellow.  Very nice, McHeath. 

[McHeath]

Did the modifications that Stephen Furley recommended.  The rectifier mod certainly helped with the popping noise in the receiver when you hang up or dial, I used a couple of diodes from Radio Shack.  The resistor on the ringer seemed to help as well, and both were pretty easy to do. 

The missus has had several conversations on it now and reports that it works fine and she is liking it.  Seems to be a pretty bulletproof phone, like our American rotaries, this one just needed a little help to make the leap into the modern phone system world. 

[Stephen Furley]

Did the modifications that Stephen Furley recommended.  The rectifier mod certainly helped with the popping noise in the receiver when you hang up or dial, I used a couple of diodes from Radio Shack.  The resistor on the ringer seemed to help as well, and both were pretty easy to do. 

The loud 'clunks' in the earpiece are unpleasant at best, and are said to be able to cause hearing damage at worst, though I would think this would probably apply mainly to people using the telephone all day long, e.g. a switchboard operator or receptionist, rather than somebody making an occasional call.  I would recommend adding either the GPO rectifier element No. 205, or a home-made alternative, to these 'phones.  I'm not sure why it wasn't included in the 706 from new, as it was in other 'phones which pre-dated it, for example the N-diagram for the Telephone No. 280 engineers test set shows it as being fitted as standard to the Mk.2 model of this 'phone, but even late versions of the 706 do not seem to have had it fitted from new, though many had it added later.

I would also recommend adding the resistor in the ringer circuit on any 'phone with the original 1k Ohm ringer (coils each marked 500 Ohm) fitted.  Not only are you likely to have problems with other 'phones wired in parallel with it, but the situation in your country is worse than it is here.  I believe your ringing Voltage is 90V, against our 75V, and your lower ringing frequency of 20 Hz. as against our 25 Hz. will also cause the ringer to draw more current than it should.

The dial speed is the same in both countries, but the break/make ratio is different, ours is 66% break, though I've not found this to be a problem with using American 'phones here; I don't think it's critical.

I'm also told that there is a difference in the signal level on the line for a given level of sound, it's higher for a British 'phone, though I haven't been able to confirm this, or find out the details.  I think this may be the case, as I cannot get a tone dialer to work reliably with American 'phones in this country, though others report that the same model of dialer, from the same Ebay seller works fine with them in America, it works fine with British 'phones here.  The result of this would be that if an American 'phone was talking to a British one the user of the American one would hear an increased sound level, which may not be a bad thing with the fall-off with the age of the equipment (and the users?), but the user of the British one would hear a reduced sound level.  If this is the case the difference seems to be only minor.

[McHeath]

As for the sound quality here, we are in AT&T landline service and the 706 seems to have the same receiving sound as the American phones.  However, I do note that it hushes background static on our one poor line in the house, the line in the office needs attention and gives static, better than all but the oldest American phones.  The WE phones with the 425 A and B networks silence the static really well, like the 706, but the newer 425 Es are not as good, and the really modern Cortelco circuit board networks do a poor job of masking the static.  (The 706 was made in 1978)

The handset cord is certainly tighter on the 706 and you have to fight it more to pull it out to use it.  Don't know if they are all like that or just this one. 

The dial is a good deal slower than on the WE ones, I've timed them and it's 1 to 2 seconds slower to return.  But it does not seem to matter in dialing and it works fine.  I've wondered if the 706 dial needs attention, but I've never yet tore into a dial as they scare me with all their little parts.

The 706 certainly is an attention getter on the missus desk, people go right over to examine it. 

[GG]

The Israeli telco used 706s for a while, and made them in Israel. 

About the slow dial:  the speed governor is similar to that found on AE dials, and the same principle applies: gently press each of the two weighted leaves in just a tiny bit, to increase the speed.  You may need a tiny screwdriver to reach in there and get to it.  Do it again if you want to increase the speed further.  Use any tiny screwdriver to pull the leaves out a bit from the side, if you sped it up to much and need to slow it back down.

These dials should be adjusted such that the return speed for the digit 8 matches a Western Electric dial returning from digit 0.  Take a look at the finger wheels and you will notice that on the WE dial fingerwheel there would be room for two more holes; on the British dials (Israeli in this case) there would be room for four more holes.  Thus a British dial dialing 8 should take as much time as a WE dial dialing 0.   There's plenty of info on these dials on the Britishtelephones site.  They are not particularly easy to disassemble, but serious disassembly isn't necessary to adjust the speed.  Just unscrew the screw holding the dial bracket to the hookswitch bracket, then unscrew the screw at the bottom of the dial that holds it into its metal bracket, and the dial unit itself will come out of the bracket.  Take off the rear protective cover and you can get at the governor pretty easily.   

Increasing the value of the resistor to which Stephen referred (the one you'd add into the ringer circuit) will enable adjusting the bells to a quieter ring.  706s as found, ring almost as loudly as SC 1543s, so quieting down the ring a bit is a good thing. 

[gpo706]

I will give all this a whirl.  How do you get the fingerhole dial ring off?

McH, bit late on a reply I know, but take some "Scotch tape" apply firmly over the centre "opal" (dial card cover) and pull and the opal should come out, remove the dial card and underneath is the centre screw for taking the fingerwheel off.

Then you have the faceplate exposed, there are two differently sized spring clips, left and right that hold it on, flick them out and it makes cleaning the exposed bits of your dial so much easier.