At our exhibition, we introduce the world of telephone exchanges with an ARK-511 type crossbar system end office.

The BHG factory was founded after the nationalization of the Standard Electric Company in 1950. In 1968 the company bought an Ericsson-license to produce relay controlled (AR-system) (village)centres, working with 30, 60 or 90 subscriber's lines depending on the configurations, and based on that they supplied the Hungarian Post Office with the necessary telephone exchanges.

In their hierarchy the ARK-511 rated as a small capacity end office, that could serve the automatic telephone traffic of smaller settlements through the connecting superior exchange.

To supply 30 terminuses one crossbar machine was used in the telephone exchange (with 10 pieces 30 output bridge), for 60 terminuses 3, and for 90 terminuses 5 such devices had to be installed.

Two digits were enough to distinguish the subscribers of the ARK-511 end office, these were  the two last digits of the dial number.

Source: Képes, Gábor - Álló, Géza: The Past of the Future (A jövő múltja), NJSZT, Budapest, 2013., p41