{{Short description|Polish telephone plug}} [[File:WT-4 & RJ11 telephone plug.png|alt=A photograph of a WT-4 plug with four metal prongs and a plastic pin protruding from the top, and an RJ-11 socket on the side. The metal prongs are labelled with the letter A, while the RJ-11 socket is labelled with the letter B.|thumb|A WT-4 plug (A) with an RJ-11 adapter (B)]] [[File:GTN-6 i GTN-4.jpg|alt=A photograph of a plastic GTN-6 socket (with seven holes) and GTN-4 socket (with five holes) side-by-side.|thumb|GTN-6 (left) and GTN-4 (right) sockets produced by Telos-Kraków.]] '''WT-4'''<ref>{{Cite book |url=https://bc.pollub.pl/dlibra/publication/7050/edition/6710 |title=Wtyczki telefoniczne typu WT-4 BN-90/3213-222/02 |date=1990 |language=pl}}</ref> (adopted as '''ВТ-4'''<ref name=":0">in Cyrillic script</ref> in the USSR<ref name=":02" />) 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{{Citation needed|date=December 2023}}. It has since been replaced by the RJ-11 standard. Sockets are labelled with the text '''GTN-4'''<ref name=":2">{{Cite book |url=https://bc.pollub.pl/dlibra/publication/7052/edition/6712 |title=Wtyczki telefoniczne typu GTN BN-90/3213-22/04 |date=1990 |language=pl}}</ref> ('''РТШ-4''' in the USSR<ref name=":02" />).
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. alt=A GTN-6 plug disassembled into two parts, the plastic cover on the left and the internal electronics on the right. Above the terminal block is visible a blue capacitor.|thumb|The inside of a GTN-6 plug. Visible above the contacts is the 1μF capacitor. A rare 6-pin version also existed, called '''WT-6'''.<ref>{{Cite book |url=https://bc.pollub.pl/dlibra/publication/7051/edition/6711 |title=Wtyczki telefoniczne typu WT-6 BN-90/3213-22/03 |date=1990 |language=pl}}</ref> 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. {| class="wikitable" |+Sockets and plugs according to Polish BN-90/3213-22<ref name=":1">{{Cite web|url=https://bc.pollub.pl/dlibra/results?q=BN+3213-22&action=SimpleSearchAction&type=-6&p=0&sf=Date|title=BN-90/3213-22 - Biblioteka Politechniki Lubelskiej|lang=en|website=bc.pollub.pl|access-date=2024-10-31}}</ref> and Soviet GOST 8810-81 standards<ref name=":02">{{Cite book |url=https://allgosts.ru/33/050/gost_8810-81 |title=ГОСТ 8810-81 (СТ СЭВ 5396-85). Розетки и вилки телефонные. Технические условия |publisher=Издательство стандартов |year=1981 |place=Москва |language=ru |access-date=2024-10-31 |archive-url=https://web.archive.org/web/20171005100349/http://allgosts.ru/33/050/gost_8810-81 |archive-date=2017-10-05 |url-status=live}}</ref> ! colspan="2" |Socket ! colspan="2" |Socket with capacitor ! colspan="2" |Plug ! rowspan="2" |Number of pins |- !BN !GOST !BN !GOST !BN !GOST |- |GTN-4 |РТШ-4 (RTSh-4) |GTN-4c |РТШК-4 (RTShK-4) |WT-4 |ВТ-4 (VT-4) |4 |- |GTN-6 |РТШ-6 (RTSh-6) |GTN-6с |РТШК-6 (RTShK-6) |WT-6 |ВТ-6 (VT-6) |6 |} {| class="wikitable" |+Socket pin-out !Function, notes ! colspan="3" |Pin number in GTN<ref name=":2" /> (RTSh<ref name=":02" />) socket !Function, notes |- |Ground. Used in sets with grounding buttons when working with internal telephone exchanges |6 (1) | rowspan="3" |center|frameless |5 (а<ref name=":0" />) |Telephone line B, in GTN-4c connected with capacitor |- |GTN-6 advanced features. Not present in GTN-4 |2 (3) |1 (4) |GTN-6 advanced features. Not present in GTN-4 |- |In a plug bridged with pin 5 (а). Used to connect an additional bell when phone plug is connected |4 (2) |3 (б, b) |Telephone line A |- |In GTN-4c connected with capacitor |8 (5) |Socket switch pins, disconnected on plug insertion |7 (6) |Permanently connected with pin 3 (б) in socket |} == See also ==
== References ==
* ''Biuletyn Informacyjny Teleelektroniki'', nr 2 / 1974 * [https://telesfor99.org/download/schemat_Aster_RWT.jpg Schemat telefonu Aster (prod. Radomska Wytwórnia Telefoniczna)] * [https://telesfor99.org/download/schemat_CB662.jpg Schemat telefonu CB-662 z podświetlaną tarczą]
== Notes == <references /> Category:Telecommunications Category:Signal connectors Category:Telephone connectors