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Old 12th Aug 2021, 9:33 am   #1
bigvito
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Default ITT Model 2500 no ring, need older PBX?

Hello, everyone. I am new to vintage telephones, I recently got an ITT Model 2500 (probably from the 70s, seems to be a common phone in the US. DTMF) which I connect to the cheapest new pbx I could get, CDX8000 from china.
It can place & receive calls, talk and listen just fine.
The ringer doesn't work. It has mechanical bells.
The phone has fours wires, but only two of them are connected.
The pbx only has two wires.

I believe the pbx is incompatible but I don't really know anything about telephones. A late 90s/00s telephone with its own power supply rings just fine, so I feel like the remaining two wires ought to be connected to something, and I need another pbx for that?

I greatly appreciate the help. Thank you
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Old 12th Aug 2021, 9:28 pm   #2
OscarFoxtrot
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Default Re: ITT Model 2500 no ring, need older PBX?

Does the phone work on a normal phone line?

Can you open the phone and put a voltmeter on the bell coils?

US phones often have a bias spring on the bell which may need to be moved or taken off, especially if your PBX is putting out a lower ringing voltage or higher ringing frequency than expected on the US network.
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Old 13th Aug 2021, 4:59 am   #3
TonyDuell
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Default Re: ITT Model 2500 no ring, need older PBX?

You can get the ITT maintenance manal from the telephonecollectors.info site. It's called the 'timm-2' manual and is a big file, almost 60MBytes.

This contains the circuit of the 2500 telephone (along with many others), exploded diagrams of the ringer, details of the ringer test set, etc.
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Old 13th Aug 2021, 10:54 am   #4
bigvito
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Default Re: ITT Model 2500 no ring, need older PBX?

I greatly appreciate the answers, I'll go do some learning and let you know.
Have a nice weekend.
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Old 13th Aug 2021, 9:24 pm   #5
dagskarlsen
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Default Re: ITT Model 2500 no ring, need older PBX?

Typical for these are that the ringer circuit has one common wire, the other has to be connected to the other line. Not sure how ITT did it on yours, that actually depending on the version of the potted network/printed network.
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Old 6th Sep 2021, 8:43 am   #6
bigvito
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Default Re: ITT Model 2500 no ring, need older PBX?

Still looking into this with some much appreciated help from dagskarlsen.

Thank you all again.
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Old 6th Sep 2021, 4:47 pm   #7
dagskarlsen
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Default Re: ITT Model 2500 no ring, need older PBX?

Try yellow and green to one line, and red to the other, the black will not be in use.
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Old 8th Sep 2021, 3:31 pm   #8
Oldcodger
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Default Re: ITT Model 2500 no ring, need older PBX?

Being an American PABX, reminds me of a problem with Panasonic PABX, where a UK ( usually BT) Fax machine would not ring as the Fax was looking for BT frequencies and Panasonic gave out a different frequency. But whoop's I've just realised that your phone has mechanical bells. Connect pins 2 & 5 via a 1.8uF capacitor to the bell and ring the number. i use to stock only master sockets in my pack and cut out the capacitors. Solder a bit of telecoms internal cable to the cap and it will go into the pins in a slave socket. That way you know if the ring problem is in phone or phone wiring. ( Bell rings like that, then phone needs investigating).

Last edited by Oldcodger; 8th Sep 2021 at 3:39 pm.
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Old 9th Sep 2021, 7:03 am   #9
dagskarlsen
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Default Re: ITT Model 2500 no ring, need older PBX?

The diagram: https://www.telephonecollectors.info...tt2575-tl/file

The ringer wires should be connected as in the diagram ,but you need to strap between yello line wire and Red line wire.

The capacitor between K and A terminals should be cose to 0-5 uF and be a bepolar one rated 200V or more. If that is defect any bipolar capacitor rated 200V or more and between 0.47 and 1.5 uF will do the job.

Mesuring each coil they will have quite different resistance, if one is broken, you may strap it until you get a new ringer. Strapping a coil, or increasing the value of the capacitor will ofcourse increase the power used for ringing, but still it will be less than the olde ringers from the pre WWii time.
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Old 9th Sep 2021, 2:16 pm   #10
bigvito
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Default Re: ITT Model 2500 no ring, need older PBX?

sorry, posted my reply not realizing there were more replies.
I'll read what you both wrote and try to figure something out.
dagskarlsen: I just realized I live less than an hour away from you, just saying.
thank you
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