Coil testing device employing a d.c. balance circuit to measure the effect of the test coil loading on a transistor oscillator

Claim 1

A COIL TESTING APPARATUS COMPRISING A TRANSISTORIZED OSCILLATOR HAVING A CURRENT SUPPLY CIRCUIT AND AN OUTPUT CIRCUIT, AND INCLUDING A PAIR OF MATCHED TRANSISTORS, SAID CURRENT SUPPLY CIRCUIT INCLUDING A SOURCE OF SUPPLY CURRENT, A COIL TO BE TESTED, SWITCHING MEANS ADAPTED TO CONNECT SAID COIL ACROSS SAID OUTPUT CIRCUIT OF SAID TRANSISTORIZED OSCILLATOR, A SERIES CONNECTED BALANCE CIRCUIT INCLUDING A D.C. SOURCE OF POTENTIAL AND A VARIABLE RESISTANCE COUPLED IN SAID CURRENT SUPPLY CIRCUIT, A SENSITIVE CURRENT INDICATING MEANS CONNECTED ACROSS SAID BALANCE CIRCUIT OF SAID TRANSISTORIZED OSCILLATOR TO INDICATE THE REACTANCE OF SAID COIL BY VIRTUE OF A CHANGE IN CURRENT FLOW THROUGH SAID CURRENT SUPPLY CIRCUIT, SAID BALANCE CIRCUIT ACTING TO BALANCE THE CURRENT IN SAID CURRENT SUPPLY CIRCUIT OF SAID TRANSISTORIZED OSCILLATOR SO AS TO PRODUCE A REFERENCE READING ON SAID SENSITIVE CURRENT INDICATING MEANS UNDER A NO-LOAD CONDITION.