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Old 11th Apr 2009, 11:52 am   #1
thaistyle
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Default Old GEC telephone TEL/51P/ATS conversion help

I have acquired a bakelite GEC telephone from Australia, which seems to be a 'spit' image of a GPO 332L inside and outside.
However, after following the 332 conversion instructions here (http://web.ukonline.co.uk/freshwater/pstconv1.htm#332) it appears that the phone requires to be wired differently.
Dial-tone is present, but when the dial is operated other phones in the house 'tinkle' and the bell doesn't ring on incoming calls.
On the base plate is a GEC sticker and this information - TEL/51P/ATS.
Any help and guidance would be appreciated.
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Old 11th Apr 2009, 2:19 pm   #2
Darren-UK
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

The site to which you linked also has a page for Australian telephones, including the No.51. Have you seen that? There's a circuit too, but seemingly no instructions for converting to British PST. Comparison between that and the GPO 332 may be helpful nonetheless. I've not actually checked to see if there are indeed many/any differences though.
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Old 11th Apr 2009, 4:41 pm   #3
thaistyle
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

Thank you for your reply and the No.51 link, I hadn't actually noticed that ref.
I have been looking mainly here, 400type.htm, because the diagram at B29 is the same as the diagram inside the phone base-plate.
But as you say, no reference on how to convert, so will have to go deeper into the circuitry and see how it goes, or discover a compatability with another model telephone which does have a known conversion.
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Old 11th Apr 2009, 5:25 pm   #4
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

Hi,
If your GEC 51 is similar to the one that Darren mentions try strapping as follows -

Before doing this check original strapping and wiring and note down so that the wiring can be restored to original connections if required

WHITE of line cord to Terminal 2 in the telephone

RED of line cord to Terminal 9

Remove strap between Terminal 10 - 11 and connect BLUE of line cord to Terminal 11

Remove strap 11 - 12 and Replace with a 3k3 0.25W resistor

GREEN of line cord is spare and should be insulated and tucked away safely inside telephone.

Regards
Andrew
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Old 11th Apr 2009, 7:09 pm   #5
thaistyle
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

Getting warmer ! I followed the suggestions from Andrew and the phone now rings on an incoming call. However, there is now no dial-tone (previously was) and lifting the receiver doesn't pick-up the call. Dialing out - nothing happens.
Should the green line-wire be connected somewhere ?
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Old 11th Apr 2009, 7:44 pm   #6
thaistyle
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

Thanks for the inspiration, phone working fine now except for one small issue.
There was quite a lot of acoustic shock in the earpiece, so I fitted a 205 rectifier across terminals 5 and 6....but now the earpiece volume is almost inaudible ?
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Old 12th Apr 2009, 10:20 am   #7
julie_m
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

Quote:
Originally Posted by thaistyle View Post
Should the green line-wire be connected somewhere ?
No, the green wire doesn't do anything.

The red and white are the actual twisted pair. Blue is connected to red via a 1.8µF capacitor in the master socket (or a 470nF capacitor in an ADSL filter). When the phone is on-hook, the bell is connected between blue and white. When the phone is off-hook, blue and white are shorted together. On a pre-ADSL system, this means all the bells are shunted and so there should be no tinkling due to the voltage changing as LD pulses are sent. On an ADSL system, with separate capacitors for each phone, there is no tinkle prevention -- but DTMF dialling as used by modern phones will not cause tinkling anyway.

The 3kΩ resistance is required because before the RJ431 plug and socket system was introduced, phones had 1kΩ bells connected in series (the 1.8µF capacitor was fitted inside one phone, and tinkle prevention worked by interrupting the bell circuit). The plug and socket system required parallel working, so a change was made to 4kΩ bells. Either way, the exchange would never see an impedance less than 1kΩ from the bell circuit.
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Old 12th Apr 2009, 11:21 am   #8
AndiiT
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

Hi,
Looking at the circuit again ensure that there is a strap/link present between terminal 2 and the unmarked Terminal (1?) which is connected to the brown wire that extends to the switch hook; if that strap is missing you will get the symptoms that you mention (ringing but no voice/ring trip when the receiver is lifted).
Leave all other wiring as suggested previously.

Regards
Andrew
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Old 12th Apr 2009, 1:21 pm   #9
thaistyle
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

Thank you Andrew, the phone is working in all respects now....except for the issue I referred to in my previous post.
ie. If I remove the 205 rectifier from between terminals 5 and 6, the clicking in the earpiece when toggling the switch-hooks is painful....but the speech volume level in the earpiece is loud and clear. With the 205 across 5/6 the clicking is greatly reduced but the speech volume is almost inaudible !
Would you happen to have a suggestion to solve this one please ?
Thanks,
Jim
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Old 12th Apr 2009, 1:40 pm   #10
AlanBeckett
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

Jim,
A couple of back-to-back diodes usually fixes it.
Alan
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Old 12th Apr 2009, 3:08 pm   #11
trevwgb
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

Hi Alan
Re the 2 diodes - that's a useful tip which I will try - have experienced the same problem with the rectifier.
Apols for ignorance here, but is there a particular component which one would use for this - and does "back to back" mean connecting the anode of one to the cathode of the other?
Thanks
Regards
Trev
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Old 12th Apr 2009, 5:10 pm   #12
AlanBeckett
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

Trev,
In parallel, but opposite ways round.
Alan
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Old 12th Apr 2009, 8:05 pm   #13
trevwgb
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Default Re: Old GEC telephone TEL/51P/ATS conversion help

That's clear
Thanks
Trev
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