“Fortress” is a nickname for the single-slot pay phone developed by the Bell System in the late 1960s. The name now applies to any style of single-slot, coin line controlled pay phone. There are 3 main variations of the “Fortress” pay phone. The original Western Electric model, used only by Bell System companies, the Automatic Electric (GTE) model, used by many independent companies, and the Northern Electric (Nortel) Centurion model, used by Canadian companies and by some USA independent companies.
Although the phones look quite different, they all operate the same way. Fortresses require a special coin line to operate properly. For local calls, the phone counts up the money until the local rate has been deposited. When a sufficient deposit is made, the pay phone completes a path to ground so that the phone will pass the coin ground test. After a phone number is dialed, the central office conducts the coin ground test, which consists of sending an electrical current to the pay phone and measuring the resistance to ground. If the resistance is infinite, the call is considered unpaid and routed to a recording telling the caller to hang up and pay before dialing again. If the resistance is around 1000Ω or less, the call is considered paid and it is put through.
Modern Pay Telephone Index
Automatic Electric Model 120 Fortress Pay Phone
Pictures and descriptions of GTE / Automatic Electric Pay Phones that were commonly found in the United States and Canada.
Northern Electric/Northern Telecom Centurion Pay Phone
Pictures and descriptions of Northern Electric / Northern Telecom Pay Phones that were commonly found in the United States and Canada.
Western Electric Fortress Pay Phone
Pictures and descriptions of Western Electric / Lucent Pay Phones that were commonly found in the United States.
Other Manufacturers of Modern Pay Phones
Pictures and descriptions of other telephone company owned modern style single slot pay phones that were in use in North America.
COCOT Pay Phones
Customer owned coin operated telephones