Restoring an old payphone 2

[Tyler62]

Hi,

A friend of mine has been recently given an old non-operating payphone(i think its a bell one from the late 80's, havent seen it yet.). He want's to restore it and hang in in his home as a fully functional phone. I'l be helping him restore it. The circuit board for it has been snapped so he has tried replacing it with newer digital phone components. He has the keypad working properly but the original reciever will not work. I'm considering swapping the new reciever components into the original reciever. The main problem is that he wants the original bell type ringer to work and not have to use the digital one from the other phone. I have experience with electronics but am not that experienced with telephones and cant say too much because i have not seen it yet. The information that ive got with regards to the ringer is that it is a 4 wire bell type ringer. My friend says that the digital can't provide enough current to ringer but i think it is more than that. If anyone could provide some insight(i know the description is vague, sorry) or knows any good site's for phone circuity, it would be greatly appreciated.
Thanks in advance

 

[OperaHouse]

If you swap everything else out, you should be able to operate the ringer by just putting a capacitor in series with the coil. Sure it would be nice to disconnect it when you pick up the reciever, but it shouldn't present that much load. I've often hooked up relays on the line through cpacitors to operate lights or outside horns without signal loss.

 

[Tyler62]

Thanks Operahouse,

What size cap do you suggest i use?

 

[OperaHouse]

Ringer is 20HZ / 150V. I'd start with 1-2 uf and just experiment.

 

[peebee]

Not that I have any idea what I'm talking about, but that never stopped me before. . . .

This site, electronics.howstuffworks.com/telephone2.htm , shows the ringer hooked directly across the line.

That may not work though, particularly with older style ringers -- this site,

http://www.navysalvage.com/2&4wire.html

, seems to indicate that the cap is required to keep the ringer from giving you a busy signal all the time as well as to avoid other problems. They're showing a 0.5MF cap, whatever MF is -- I assume that means .5mF, which would be 500uF, but maybe they really mean 0.5uF, which would be more in line with OperaHouse's recommendation. And he definitely knows more about this stuff than me.

Realize in either case above, you'd be driving the ringer directly off the phone line, not off the ringer circuit in your digital phone. You'd just want to shut the digital phone's ringer off or disconnect it or something and drive your bell off the phone line.

Here's some nice background information on the electrical characteristics of the phone line with respect to driving a ringer:

http://www.hut.fi/Misc/Electronics/circuits/telephone_ringer.html

Last but certainly not least, this PDF, "Old Telephones -- How to Repair and Rebuild Them", at

http://www.telephonetribute.com/pdf/rpr_ot21.pdf

, would seem to not only tell you how to get your ringer working, but how to rebuild the whole original phone if you were so inclined. Found that thru links from

http://www.telephonetribute.com/technical_information.htm

and bellsystemmemorial.com/references.html .

Lucky for you, there's LOTS of information freely available on this stuff. Try a Google search on "4-wire telephone antique schematic", that's how I came across much of the above sites.

Hope this helps.