Automatic replacement of a faulty amplifier

Claim 2

Apparatus for automatically changing amplifiers in a public address system comprising a microphone; a loudspeaker, a first amplifier connected to the microphone and loudspeaker; a second amplifier; an audio frequency signal source connected to the microphone input of the second amplifier; a power source; means for connecting the power source to energize the first amplifier; means responsive to the first amplifier supply current exceeding a predetermined level for disconnecting the microphone and loudspeaker from the first amplifier, for connecting the microphone and loudspeaker to the second amplifier, and for connecting the power source for a predetermined interval to the second amplifier and the signal source; and means connected to the loudspeaker output of the second amplifier and responsive to the amplification of the signal by the second amplifier at the end of the predetermined interval for retaining connection of the power source to the second amplifier when the amplification is above a predetermined level.

Claim 3

Apparatus according to claim 1 in which the means responsive to the amplification of the signal by the second amplifier includes means for disconnecting the microphone and loudspeaker from the second amplifier when the amplification is below the predetermined level.

Claim 4

Apparatus according to claim 2 in which the means for disconnecting the microphone and the loudspeaker from the first amplifier and for connecting the microphone and the loudspeaker to the second amplifier includes means for disconnecting the first amplifier from the power source when the supply current exceeds a predetermined level, a tripping relay coil connected to the power source through the means for disconnecting the first amplifier and having first and second normally closed contacts, a time delay relay coil connected to the power source through the first normally closed tripping relay contact and having a first normally closed contact, a first latching relay trip coil connected to the first normally closed tripping relay contact through the first normally closed time delay relay contact and the second normally closed tripping relay contact and having trip contacts connecting the microphone and the loudspeaker to the first amplifier and reset contacts connected to the microphone and loudspeaker, and a second latching relay trip coil connected to the first normally closed time delay relay contact and having trip contacts connecting the first latching relay reset contacts to the second amplifier. Apparatus according to claim 3 in which the signal source includes a direct current power supply and an oscillator connected to the direct current power supply.

Claim 5

Apparatus according to claim 4 in which the means for connecting the power source for a predetermined interval to the second amplifier and the signal source includes a second normally closed time delay relay contact connected to the first normally closed time delay relay contact, a power relay coil connected to the second normally closed time delay relay contact and having a normally open contact connecting the power source to the second amplifier, and an oscillator relay coil connected to the first normally closed time delay relay contact and having a first normally open contact connecting the power source to the direct current power supply and a second normally closed contact connecting the direct current power supply output to the oscillator.

Claim 6

Apparatus according to claim 5 in which the predetermined interval is established by a time delay between the energization of the time delay relay coil and the actuation of the time delay relay armature.

Claim 7

Apparatus according to claim 6 in which the means responsive to the signal amplification above a predetermined level includes a test relay having a normally open contact, a transistor having its base and emitter connected to the loudspeaker output of the second amplifier, and its collector and emitter connected in series with the direct current power supply and the test relay coil, a normally open time delay relay contact, and a third latching relay trip coil connected to the power source through the normally open test relay contact and having a trip contact connecting the power relay coil to the first normally closed tripping relay contact through the normally open time delay relay contact.

Claim 8

Apparatus according to claim 7 in which the means responsive to the signal amplification below a predetermined level includes a second latching relay reset coil for opening the second latching relay trip contacts when the coil is energized, and a third latching relay reset contact connecting the second latching relay reset coil to the normally open time delay relay contact.

Claim 9

Apparatus according to claim 8 including means connecting the power source to the reset coils of the latching relays.

Claim 10

Apparatus according to claim 9 which includes at least one additional amplifier connected to the power source with a microphone and a loudspeaker associated with each amplifier; a tripping relay associated with each amplifier and connected to the power source and the time delay relay; A latching relay associated with each amplifier connecting each microphone and loudspeaker to the associated amplifier and the second latching relay and connected to the associated tripping relay; and means connecting the power source to the reset coils of the latching relays.