The Speech Network is an important and poorly understood part of the telephone. The network serves a number of important functions:
- Controls side tone - Side tone is hearing your own speech in your ear when you talk. It is important to provide some side tone to confirm the phone is working but it is also important to keep the level low so that the user does not talk more softly upon hearing his own loud voice in his ear.
- Directs most of the speech energy out on the line towards the other stations.
- Regulates the amount of current that the phone draws from the battery feed coil. This is important in situations like our model railroads where multiple phones are off hook at once. It also prevents excessive current from going through the transmitter,
- Provides a handy terminal block on which to connect all of the components of the phone
I strongly recommend that all phones use a speech network. On earlier or non-WECo models, there may be an exposed transformer and some external components that provide this function.
System performance is better when all stations draw the same amount of current, so standardize if possible. You can retrofit most period phones to use modern speech networks and I recommend you do so.
These are used telephone networks which are type 425 or compatible. This is the speech network used in classic Western Electric, ITT, and Stromberg Carlson telephones from the 50s until de-regulation in the 80s. You need one of these per telephone. If you can find a Western Electric 554 or 2554 wall set, one of these is in it, but if you're building your own phones into the fascia, these are handy! See the telephone application notes. Note these networks use spade lug terminals, so you will need to get spade tipped lugs such as Radio Shack 6403070 to make connections.