WT-4 (adopted as ВТ-4in Cyrillic script in the USSR) is a Polish telephone plug used to connect telephone sets to the network. Introduced in the second half of the 20th century and adopted in several Eastern Bloc countries as a standard. It has since been replaced by the RJ-11 standard. Sockets are labelled with the text GTN-4 (РТШ-4 in the USSR).
WT-4 plugs consist of 4 metal pins with an additional plastic pin at the bottom to prevent inserting the plug the wrong way round. When the plug is inserted into a socket, the plastic pin also disconnects a 1μF capacitor built into the socket. When connected, the capacitor simulates a telephone set with the handset hung up. This allows for the testing of the line even when the subscriber doesn't have a telephone connected to the network. In the mid-1990s, installations of WT-4 plugs began to be phased out, and the standardized shape of the socket was used to install RJ-11 connectors instead.
A rare 6-pin version also existed, called WT-6. Extra pins (numbered with the missing 1 and 2) were located between the existing pins 3 and 5, and 4 and 6, respectively. These extra pins were used for powering telephone sets with illuminated rotary dials, as well as some more advanced telephone installations. +Sockets and plugs according to Polish BN-90/3213-22 and Soviet GOST 8810-81 standardsSocketSocket with capacitorPlugNumber of pinsBNGOSTBNGOSTBNGOSTGTN-4РТШ-4 (RTSh-4)GTN-4cРТШК-4 (RTShK-4)WT-4ВТ-4 (VT-4)4GTN-6РТШ-6 (RTSh-6)GTN-6сРТШК-6 (RTShK-6)WT-6ВТ-6 (VT-6)6 +Socket pin-outFunction, notesPin number in GTN (RTSh) socketFunction, notesGround. Used in sets with grounding buttons when working with internal telephone exchanges6 (1)5 (а)Telephone line B, in GTN-4c connected with capacitorGTN-6 advanced features. Not present in GTN-42 (3)1 (4)GTN-6 advanced features. Not present in GTN-4In a plug bridged with pin 5 (а). Used to connect an additional bell when phone plug is connected4 (2)3 (б, b)Telephone line AIn GTN-4c connected with capacitor8 (5)Socket switch pins, disconnected on plug insertion7 (6)Permanently connected with pin 3 (б) in socket See also
Telephone jack and plug
References
Biuletyn Informacyjny Teleelektroniki, nr 2 / 1974 Schemat telefonu Aster (prod. Radomska Wytwórnia Telefoniczna) Schemat telefonu CB-662 z podświetlaną tarczą
Notes