Author Topic: Wiring 3-wire vs 4-wire handset on SC 1248WI  (Read 2877 times)

Offline MDK

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Wiring 3-wire vs 4-wire handset on SC 1248WI
« on: February 04, 2012, 08:33:32 AM »
I just acquired an SC 1248WI magneto "Frankenphone". It has a WE handset, much like the one on my 302, but it looks like the wiring from the transmitter to the receiver is concealed. It's marked 1248WI SPECIAL, and through the clear window on the bottom it says, "65 C" and "934". The network is marked "200595 B"

The magneto was frozen when I got it, but with a drop of sewing machine oil and some fiddling, it works. The ringer rings when I turn the magneto, both on-hook and off-hook. Is that right?? It will also ring another phone with their line cords directly connected.

When connected with a battery to another phone, I can hear voice from the other phone, but not vice-versa. I swapped out a working transmitter element just to see if that might be the problem. On the POTS line I get no dial tone.

I drew myself a diagram of how this is wired and it appears NOTHING like the wiring diagrams I found online.

I believe the network is the correct one for this phone, but the wiring seems to be fairly hosed up. The wiring diagram shows a 4-wire handset. Is there a way to wire this with a 3-wire handset so it will work properly? My intent is to use this phone with another for an intercom. I may have to just find another 4-wire handset, but was hoping to use what I have on hand.

Any clues would be helpful.



Offline MDK

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Re: Wiring 3-wire vs 4-wire handset on SC 1248WI
« Reply #1 on: February 04, 2012, 09:52:06 AM »
If I were to rewire the phone based on the attached diagram, terminal 8 would have no purpose, as I'm using a 2-wire line connection. Could the blue wire shown from the transmitter be made a common, and if so, which wire of the handset would be common (red or green)?

Offline dsk

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Re: Wiring 3-wire vs 4-wire handset on SC 1248WI
« Reply #2 on: February 04, 2012, 11:20:40 AM »
Not easy to read these old diagrams, but this has a least a common between receiver and transmitter:
http://tinyurl.com/6nt3k2p

And yes it should be able to generate a ring in both on and off hoock state, but it should short out its own ringer when cranked. May need some more oil, and cleaning of the contacts.

dsk

I have even got a regular New York number :-) 646 570 1796

Offline MDK

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Re: Wiring 3-wire vs 4-wire handset on SC 1248WI
« Reply #3 on: February 04, 2012, 11:32:38 AM »
I found that right after I posted. I rewired it based on the bottom schematic. I think not having a separate battery is the problem. I've got a 9V battery and resistor wired in series between two phones.

What would be the best way to convert this to a common battery type system?
« Last Edit: February 07, 2012, 07:57:49 AM by MDK »

Offline MDK

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Re: Wiring 3-wire vs 4-wire handset on SC 1248WI
« Reply #4 on: February 04, 2012, 12:48:44 PM »
Well, seems I figured it out. I checked all my wiring and discovered I had mistakenly written down my handset wiring colors. Swapped the yellow and green in the handset and it works.

It's wired mostly based on the bottom diagram that Dag had linked. I jumpered between L2 and what had been batt+.

Thanks, Dag! This is why I love this place.

Offline dsk

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Re: Wiring 3-wire vs 4-wire handset on SC 1248WI
« Reply #5 on: February 04, 2012, 12:54:26 PM »
I love to figure out solutions like that.
Better than Sudoku or x-words.

I guess I have a solution for your CB wish too.
Just rewire after this: http://tinyurl.com/7e3hrpf

dsk

I have even got a regular New York number :-) 646 570 1796

Offline MDK

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Re: Wiring 3-wire vs 4-wire handset on SC 1248WI
« Reply #6 on: February 04, 2012, 01:01:00 PM »
Thanks, I'll try that.

Offline MDK

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Re: Wiring 3-wire vs 4-wire handset on SC 1248WI
« Reply #7 on: February 04, 2012, 01:46:56 PM »
It's a lot more fun than sudoku.

I rewired it by the last drawing you linked. Voice sounds much clearer connected that way.

Offline dsk

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Re: Wiring 3-wire vs 4-wire handset on SC 1248WI
« Reply #8 on: February 07, 2012, 12:41:57 PM »
This made me do a lot of thinking ;D
(No I doesn't hurt ;D)
The speech network used in a lot of SC phones. e.g. 1443, 1244, 1248, 1258, 1243,1250 and probably many more are the most genius network for a hobbyist I ever studied. (At least at the paper  :P)
It is as near as the network used in the WE 500 series and later as possible but without automatic loop compensation. This i even universal for local battery or common battery operation :D :D
It could be used in a subset, for almost any telephone needing a subset. ;D

Maybe not the right thread to ask, but dos it sound (work) that well to?

dsk

I have even got a regular New York number :-) 646 570 1796

Offline MDK

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Re: Wiring 3-wire vs 4-wire handset on SC 1248WI
« Reply #9 on: February 07, 2012, 03:20:09 PM »
I am amazed at how many different ways are shown to wire this same network for different applications.

It works well. The sound would probably be a bit better with a WE type G handset. I've always thought they sounded better than the F type, even though this might start a war over which sounds better.

I'm wondering, what is the proper handset for the 1248WI? My SC1543 is also missing the correct handset (it has an AE handset). Are SC handsets rare, or just not very good?

Offline MDK

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Re: Wiring 3-wire vs 4-wire handset on SC 1248WI
« Reply #10 on: February 08, 2012, 07:10:39 PM »


Just a quick spraypaint job, and buffed up the handset... and it's a bit more presentable. My wife doesn't hate it anymore.

I'm curious, does this have a WE dial blank? I haven't seen any other photos of this type phone with this style of blank.

« Last Edit: February 08, 2012, 07:17:47 PM by MDK »