685A verses 684A

[dennisjnunes]

what is the main difference I have been told the 685A has a network o.k. what is a network ? how do you test a subset ? I have a lot of questions but I'll wait until I figure out how you work all the different things on your forum, I'm not being snooty I just don't know what I'm doing yet. Dennis

[poplar1]

Both the 685A and 684A subsets contain the parts needed for ringing + the parts needed for speech when used with a separate transmitter, receiver, hookswitch and optional dial.

The 684A has a separate induction coil (transformer) and condenser (capacitor). In the 685A, these two components and other components are contained in a metal can with terminals on top; this is called a 425-type network.

The 684A is older technology, resembling the parts of a 302 telephone. The 685A has the same parts found in a 500 set.

Normally, a 684A is used with phones like 202s, 211s or 151ALs. A 685A can be used but it requires wiring changes in the phones. Normally, there are 4 wires from the phone to a 684A subset and 5 wires from the phone to a 685A subset.

The 685A was often seen installed with the 233G 3-slot pay phones. Since 211s were manufactured until the 1970s, the 685A was also used with these later.

[Phonesrfun]

If you really want to learn about telephony and how they work, you should get Ralph Meyer's book on telephones.

There are several other resources out there too, if you want to take the time to read up.  One is Colin Chamber's website which is

www.oldphoneguy.net ( dead link 03-18-22 )

In the left margin choose Big Books, and then from that page select the Fundamentals of Telephony - Army Manual

That book is a downloadable pdf that has some great information in it.