Five-stage amplifier Q1-5 amplifies both control signals, 38. 285 kc and 41. 805 kc, while Q6 and Q7 operate as class B detector-amplifiers to eliminate need for separate diode detectors. Desired control frequency energizes only one coil of double-fulcrum motor control relay. while noise acts on both coils and keeps relay balanced. -Transistor Amplif
ier Controls Remote Appliances, Electronics, 34:21, p 59.