Absolutely Beautiful 1970/83 GPO 746 Red

[LM Ericsson]

This Christmas I got this nice red 746 Dated 1/70 and has a sticker that reads "RE 83", which tells me it was refurbished in 1983. I can tell the dial is a later one because it has the plastic components inside. Has the nice red line cord and it even has the nice little connection block on the cord as well!!! It took me all day to restore and everything works perfect........except the ringer, which does not work at all.  I know it is possible to have the ringer work in the States with further modifications. I would absolutely appreciate if someone would help me get this absolutely beautiful telephone to ring again!!!!!!

[Adam]

Very nice!  I'm jealous, I'd love to have one like this!

[twocvbloke]

Very nice phone indeed, they're popular with some buyers & collectors cos of the colour, I keep looking at red 706 and 746 phones myself...

As for the no-ring issue, as the phone has it's original BT-52A (the connection block), I'm guessing it's unconverted and has the original wiring internally, so, you need to check inside the terminal block and look to see if there's a strap between the White and Green wires (White is the "A" wire, and Green the Ring wire), if there is no strap, just move the Green wire onto the White wire's terminal...

To wire on a US line cord, you need to use two wires only, the Green and Red wires, you connect the Red wire to the 746's White wire, and the Green wire to the 746's Red wire, that should get it to work, and as above, make sure there's a connection to the Green Ring wire (on Converted models, the Blue wire is the Ring wire and Green is Ground, which gets confusing!!)...

Should look something like my sliced & diced Modularised BT52A below, ignoring the Black and Yellow wires on the Modular side (and you don't need to put in a modular socket!!)...

You might also want to check the wiring inside the phone, comparing it to the N Diagram for the 746 range:
(PDF File link)

Hope this helps...

[twocvbloke]

Oh, I just noticed the dial label, is that what it came with? If so, then that would indicate that it used to live attached to a PBX, with the Dial 9 for Exchange line, and 9999 for the emergency services...

[LM Ericsson]

Oh, I just noticed the dial label, is that what it came with? If so, then that would indicate that it used to live attached to a PBX, with the Dial 9 for Exchange line, and 9999 for the emergency services...

The dial label is not original, I printed it off of telephonearchive, and covered the exchange name.

[LM Ericsson]

Do I need to install an extra capacitor for the ringer to work. It is what I heard.

[LarryInMichigan]

Can you post a picture of the inside of the phone so we can what what is there?  If the phone does not have a capacitor, you can buy one at Radio Shack.

Larry

[LM Ericsson]

Here's a look inside,

[twocvbloke]

I typed out a completely different post, but it seems I got things wrong... 

Anyway, the phone is definitely unconverted, so should be easy to sort out, just looking at it though, someone has cut out Capacitors C1 and C2, by removing the strap between T6 and T7, and have added a strap between T17 and T18 (has the same effect as joining the Green and White wires together in the terminal block), so this'll need sorting out...

So, it seems all you have to do is add a strap between T6 and T7 to restore connection to the capacitors, and remove the Green and Blue wires from T4 and T5 respectively and connect those to T14 and T15 to effectively insulate them (T11 thru T15 are spare terminals not connected to anything)...

Just a note, GPO phones suffer from what is known as "Bell Tinkle" in this state, due to the way that the GPO came up with the 3-wire system, so if connected to the same line as say a WE500, dialling on the WE would cause the 746 bell to "Tinkle" with every pulse...

You also might need to replace the strap between T4 and T5 with a 3.3K resistor if your phones on the same line stop ringing or the GPO phone is the only one to ring, but check first before fitting as I haven't a clue what changing the Impedance on the bells would do on a US/Canadian phoneline...

I fiddled with your photo to show what the phone needs (minus adding the resistor), this should get it to ring... 

[LM Ericsson]

Thank you. I could live with bell tinkle. It gives it character!!!

[twocvbloke]

No problem, hope you get it working...

[GG]

I have one just like it next to my bed, on the emergency extension on my PBX. 

What to do about bell tinkle:

Measure your ringing voltage.  Let's say it's 90 volts (central office; as compared to e.g. 75 volts or less from some PBXs).  Now get two 72-volt Zener diodes rated at 1 watt or more (or get four rated at 1/2 watt or more).   The generalization is, you want the zener diodes at a rating that's considerably above the normal line voltage, but below the ringing voltage. 

Wire them "back to back" so they face in opposite directions.  Install them across the terminals in the phone where you would otherwise have installed a plain strap.  Useful to add a dropping resistor too, which will reduce the loudness of the ring to a more acceptable (quieter) level. 

Here's what happens:

Dial pulses from other phones don't cause high enough spikes of DC to trigger the zener diodes and get through to the ringer coils.  However, ringing voltage, being higher than the rating of the zener diodes, causes them to trigger ("avalanche") and allow all of the voltage to pass through and get to the ringer coils, thereby ringing the bells.

An old friend of mine used to use thermistors for this, though I am not certain of the value.  The result was similar to a Trimphone: a ring that started out quiet and then got louder. 

[LM Ericsson]

The phone is ringing now. It sounds great. I kinda like the bell tinkle...

[twocvbloke]

The phone is ringing now. It sounds great. I kinda like the bell tinkle...

That's good to hear, we just got a new phoneline (at long last) and I'm awaiting someone calling so I can hear my phones ringing for the first time in about 2 months!!! 

I did find that my Ivory GPO 746 can't break dial tone though, but I think that's just down to it's dodgy dial (stripped, cleaned, lubed and adjusted, and it's still too slow at pulsing!!)...

[GG]

746s use "trigger dials" (type 21 and later if I recall correctly).  It's really easy to see if the dial is not sending pulses, and the mechanism is basically foolproof.

"Dial is too slow" can be determined easily: get another phone with a known-correct dial, wind both of them up to 0, release both simultaneously, and observe: they should both come to rest at the same time.  If the questionable dial is slower, repeat the test, winding it up to 9 and the reference dial to 0, and see if they match.  If the questionable dial is still behind, wind it up to 8 and the reference dial to 0, and see if they match.  Etc.   Dial speeds of 9 - 11 pulses per second are within specification, anything slower than 9 pulses per second may be a problem.

Speeding up GPO dials is easy: they use a highspeed governor and all you need do is *gently* press each "wing" of the governor inward just a little (using a fingertip) and then re-test for speed.   (To slow down a GPO dial, insert a small screwdriver between each governor wing and the governor axle, toward the top of the wing where it is joined to the axle, and use it to gently pry the wings outward just a little, and then re-test for speed.)

However, what I think is happening is, two or more of the wires to the dial contacts are reversed.  First try reversing the connections to the impulse contacts.  If that doesn't solve it, reverse the connections to the off-normal contacts.  If that doesn't solve it, then go back and put the wires to the impulse contacts back the way they were.  Or go look up the N-diagram on the Britishtelephones site and trace the wiring (which is easy on 746s), making sure that the wires are on the correct screws on the terminal board as well as on the dial itself. 

IMHO, 746s are as easy to work on as 500s, and GPO dials are as easy to adjust as AE dials.