Balanced gain control circuit

Claim 1

A GAIN CONTROL CIRCUIT COMPRISING FIRST AND SECOND AMPLIFYING DEVICES EACH HAVING CURRENT-EMITTING, CURRENTCOLLECTING AND CONTROL ELEMENTS, A LOAD IMPEDANCE COUPLED IN SERIES WITH THE CURRENT-COLLECTING ELEMENT OF SAID SECOND AMPLIFYING DEVICE, FIRST MEANS CONDUCTIVELY CONNECTING BOTH SAID CURRENT-EMITTING ELEMENTS TOGETHER, SECOND MEANS FOR APPLYING A UNIDIRECTIONAL OPERATING POTENTIAL ACROSS SAID FIRST MEANS AND BOTH SAID CURRENT-COLLECTING ELEMENTS, SAID LOAD IMPEDANCE BEING COUPLED IN SERIES WITH SAID SECOND MEANS AND SAID SECOND CURRENT-COLLECTING ELEMENT, THIRD MEANS FOR APPLYING IN ALTERNATING SIGNAL ELEMENT, THIRD MEANS FOR APPLYING IN ALTERNATING SIGNAL TO THE CONTROL ELEMENT OF SAID SECOND DEVICE, A SIGNAL OUTPUT CIRCUIT COUPLED TO SAID LOAD IMPEDANCE AND PROVIDING A SIGNAL IN RESPONSE TO CURRENT CHANGES THROUGH SAID LOAD IMPEDANCE, THIRD AND FOURTH AMPLIFYING DEVICES EACH HAVING CURRENT-EMITTING, CURRENT-COLLECTING AND CONTROL ELEMENTS, FOURTH MEANS CONDUCTIVELY CONNECTING THE THIRD AND FOURTH CURRENT-EMITTING ELEMENTS TOGETHER, SAID FIRST AND FOURTH MEANS BEING CONDUCTIVELY CONNECTED TOGETHER, THE FIRST AND THIRD-CURRENT-COLLECTING ELEMENTS BEING CONNECTED TOGETHER, THE SECOND AND FOURTH CURRENT-COLLECTING ELEMENTS BEING CONNECTED TOGETHER, THE SECOND AND THIRD CONTROL ELEMENTS BEING CONNECTED TOGETHER, MEANS FOR APPLYING A REFERENCE BIAS POTENTIAL TO SAID SECOND AND THIRD CONTROL ELEMENTS, THE FIRST AND FOURTH CONTROL ELEMENTS BEING CONNECTED TOGETHER, AND A CONTROL VOLTAGE INPUT CIRCUIT COUPLED TO SAID FIRST AND FOURTH CONTROL ELEMENTS FOR APPLYING A CONTROL BIAS THERETO.