Circuit for preventing accidental erasure of clock signals

Claim 1

IN A SYSTEM WHEREIN A MAGNETIC DRUM HAS A TRACK SET ASIDE WITH SIGNALS RECORDED THEREON WHICH ARE TO BE READ BY A READING HEAD HAVING FIRST AND SECOND OUTPUT TERMINALS, A PROTECTIVE CIRCUIT FOR PREVENTING ACCIDENTAL ERASURE OF SAID SIGNALS COMPRISING MEANS CONNECTED IN SERIES WITH SAID READING HEAD FOR SUBSTANTIALLY ATTENUATING SIGNALS HAVING A FREQUENCY BELOW THE FREQUENCY OF SAID RECORDED SIGNALS AND FOR SUBSTANTIALLY PASSING SIGNALS AT THE FREQUENCIES OF SAID RECORDED SIGNALS, MEANS CONNECTED IN SHUNT WITH SAID READING HEAD FOR PRESENTING A HIGH IMPEDANCE TO SIGNALS BELOW A PREDETERMINED LEVEL AND FOR PROVIDING SUBSTANTIALLY A SHORT CIRCUIT TO SIGNALS EXCEEDING SAID PREDETERMINED LEVEL, AND MEANS CONNECTED IN SERIES WITH SAID READING HEAD FOR LIMITING THE LEVEL OF CURRENT WHICH CAN FLOW IN THE PRESENCE OF A VOLTAGE AT SAID PREDETERMINED LEVEL TO A VALUE WHICH IS SUFFICIENTLY LOW TO LEAVE SAID RECORDED SIGNALS SUBSTANTIALLY UNAFFECTED.