Before it can be used on the modern plug and socket arrangements a vintage telephone needs to be converted. This involves little more than fitting a new line cord with a plug but it's quite an important "Little more."
There are plenty of web-sites saying how to do this but a lot assume that the 'phone hasn't been messed about with in the past. The following ones have diagrams showing full details how things should be done.
This shows the details of the 332 — the big chunky Bakelite ones from the 1940s and 1950s — and this the 700-series — the plastic ones from the 1960s to 1980s.
A lot of sites will say you need to fit a 3.3kΩ resistor in series will the bell motor. In the old days bell motors had two 500Ω coils, making 1kΩ in total, and if you had more than one 'phone the bells would be connected in series. When the new plugs and sockets were introduced in the 1980s this changed to bell motors having two 2000Ω coils, so 4kΩ total, and these would be connected in parallel. The resistor is to convert the old ones to the new value. If you're working on a late 'phone with 2000Ω coils you don't need it.
It's debatable how much good they do in any case. Adding one will change the DC resistance but it's AC impedance that really matters. Whether you need one of not depends on things like how many 'phones you have connected in total and how far you are from the exchange. If you find one or more 'phones doesn't ring properly, of not at all, you need the resistor. If everything works you don't, though one will do no harm.
The standing advice is to put it between two terminals but if you can solder I've found the best thing is to remove the wire that connects the two bell coils and replace it with the resistor. This is neater and there's also no chance of it accidentally touching adjacent terminals.
There are plenty of web-sites saying how to do this but a lot assume that the 'phone hasn't been messed about with in the past. The following ones have diagrams showing full details how things should be done.
This shows the details of the 332 — the big chunky Bakelite ones from the 1940s and 1950s — and this the 700-series — the plastic ones from the 1960s to 1980s.
A lot of sites will say you need to fit a 3.3kΩ resistor in series will the bell motor. In the old days bell motors had two 500Ω coils, making 1kΩ in total, and if you had more than one 'phone the bells would be connected in series. When the new plugs and sockets were introduced in the 1980s this changed to bell motors having two 2000Ω coils, so 4kΩ total, and these would be connected in parallel. The resistor is to convert the old ones to the new value. If you're working on a late 'phone with 2000Ω coils you don't need it.
It's debatable how much good they do in any case. Adding one will change the DC resistance but it's AC impedance that really matters. Whether you need one of not depends on things like how many 'phones you have connected in total and how far you are from the exchange. If you find one or more 'phones doesn't ring properly, of not at all, you need the resistor. If everything works you don't, though one will do no harm.
The standing advice is to put it between two terminals but if you can solder I've found the best thing is to remove the wire that connects the two bell coils and replace it with the resistor. This is neater and there's also no chance of it accidentally touching adjacent terminals.
