Signal switching apparatus with interlock circuitry

Claim 1

IN AN APPARATUS FOR SELECTIVELY SWITCHING BETWEEN A PLURALITY OF SIGNAL SOURCES AND A COMMON UTILIZATION CIRCUIT, SAID APPARATUS COMPRISING A PLURALITY F RELAYS ASSOCIATED RESPECTIVELY WITH SAID SOURCES AND EACH HAVING SWITCHING CONTACTS CLOSABLE TO CONNECT THE ASSOCIATED SIGNAL SOURCE TO SAID UTILIZATION CIRCUIT AND EACH ALSO HAVING LOCKING CONTACTS CLOSABLE TO A SOURCE OF LOCKING VOLTAGE TO MAINTAIN ENERGIZATION OF THE WINDING OF AN OPERATED RELAY WHEREBY TO MAINTAIN CLOSURE OF THAT OPERATED RELAY''S SWITCHING CONTACTS, AND A PLURALITY OF SELECTOR SWITCHES ASSOCIATED RESPECTIVELY WITH SAID RELAYS AND OPERABLE TO SELECTIVELY CONNECT A SOURCE OF OPERATING VOLTAGE TO ENERGIZE THE WINDINGS OF THE ASSOCIATED RELAYS; RELAY HOLDING AND RELEASING APPARATUS COMPRISING: A TRANSISTOR HAVING OUTPUT AND CONTROL ELECTRODES; MEANS TO APPLY A FORWARD BIASING VOLTAGE TO A CIRCUIT INCLUDING SAID CONTROL ELECTRODE SO AS TO RENDER SAID TRANSISTOR NORMALLY CONDUCTIVE OF CURRENT IN A CIRCUIT INCLUDING SAID OUTPUT ELECTRODE; MEANS TO APPLY A REVERSE BIASING VOLTAGE TO SAID CIRCUIT INCLUDING SAID CONTROL ELECTRODE UPON THE OPERATION OF ANY ONE OF SAID SELECTOR SWITCHES TO RENDER SAID TRANSISTOR NON-CONDUCTIVE OF CURRENT IN SAID CIRCUIT INCLUDING SAID OUTPUT ELECTRODE; AND