We haven't had a telephone thread for a while, so here are some pictures of an old G.P.O. type 332 telephone which has just come to me for a cleanup and rewiring to work on a modern jack.
The 332 was the standard G.P.O. desk phone from the 1930s right up until the modern plastic-cased 700 series displaced it in the 1950s. Black was the most common color, as seen here, but ivory, red, and green versions were also made.
Some had a pull-out plastic tray fitted in the base, which was used to contain the dialing instructions and local routing codes. This particular unit doesn't have the tray, hence the blanking plate you can see on the front.
The dial on this phone is the type with just figures. Dials fitted to the 332 for use in London and the other director cities, as well as some other areas when STD arrived had letters as well.
[This message has been edited by pauluk (edited 04-19-2005).]
The later 700 phones had everything fixed to the base and the top part was then just a cover (much like the Western Electric 500). These earlier phones, however, just had a cover plate for the base with all the works fixed inside the top part of the casing.
And for all you sharp-eyed viewers, can you spot the one item here which is not original G.P.O. issue?
Like many of the old G.P.O. telephone sets, this phone was made by Standard Telephones in North London (my mother worked there for a while):
Electrically, the 332 set predates the use of regulators, so the internal circuitry is quite simple. Here's the schematic from inside the base plate:
#142972 - 04/19/0506:13 PMRe: Old G.P.O. Telephone
Paul, Good pictures!. I remember my Grandparents had a phone exactly like this one in thier house. Telecom NZ used to buy phones from BT if I'm right at all. Although the numbers on the dial were around the other way (1-0). Them wires from the dial unit to the base unit look like you could run an iron through them. You don't get circuit diagrams like that anymore with gear. BTW, Paul, what function did the Induction coil serve?. Arend, That may be rubber tape that you are looking at there, it's still used on some iron flexes here as cushioning under the cord grip of the appliance. As I remember Paul, your telephone number was written on a small disc of paper that fitted under a plastic disc in the centre of the dial. These phones are pretty rare here now, as being made of alabaster (like bake-lite) they often didn't survive being dropped onto hard surfaces. Could be fun fitting a BT connector to the end of that braided flex.
#142974 - 04/20/0508:54 AMRe: Old G.P.O. Telephone
No, that isn't modern heatshrink on the dial cord. It's the old type of sleeving, hard to describe, but like a braided rubber, and quite original.
The induction coil forms part of the anti-sidetone circuit. It couples audio to the receiver, and also reduces the volume of the callers own voice in the earpiece, which would otherwise be loud compared to the incoming audio from the distant end.
As I remember Paul, your telephone number was written on a small disc of paper that fitted under a plastic disc in the centre of the dial.
Not me Marc, this is exactly how it came to me so I haven't done anything to it yet.
But you've got it -- The line cord is not the original. If you look at the photo of the underside of the chassis, you can see the difference.
The original handset cord (top terminals) has a distinctly brown braid, while the line cord (bottom terminals) has a more purple color. It's actually a length of old-style twin lighting flex, probably 1950s. Not an exact match, but somebody obviously thought it better than modern PVC!
If you look at the schematic, you'll see that the original cord was a 3-wire type, although on a regular single-party line the bell return was just strapped to one side of the line on the wall junction.
Look back at the terminals on the underside of the chassis, and you can see the wire has been extended from the bottom left terminal to the one directly above it to get the bell to work. That's where the third wire would have been connected originally (compare with the "official" straps on the terminals to the right).
#142977 - 04/21/0508:42 AMRe: Old G.P.O. Telephone
Found on 1930s/40s irons and other heating appliances!
Ditto here, not that that's surprising.
Could you wire it to an old GPO headphone jack style connector?
Yes, that's what I meant when I said a 1/4-inch jack. And although the majority of single phones in homes were hardwired back in the days when this set was commonly used, those which were on a portable plan would have used just such a jack.
Personally, I think the old GPO jacks were far superior to the modern modular BT plugs, but of course these days everything is done on the basis of how cheaply it can be made.
#142979 - 04/21/0507:42 PMRe: Old G.P.O. Telephone
Actually Paul, modifying a 332 to work on modern style phone jacks is quite easy [although technically illegal]. Remove strap 10-11, and hook the bell wire which is usually the blue one these days, to terminal number 11, leaving the line pair right where they are. That way, the capacitor in the phone jack replaces the 2 microfarad cap. I don't know how hot BT are on this anymore, they *used* to insist everything complied to BS something or other, but these days it seems pretty much standard to use north amercian equipment, with my ADSL microfilters, even down to an RJ11 jack on the filter instead of the BT type. I see this as a good thing, we both know the US and Canadian systems are better right? Speaking of old jacks, the 316 switchboard plugs are *incredibly* well made by modern standards, the things are a pleasure to connect to. Pity nothing uses 1/4 inch connectors anymore.