GC166 /QP166 Valve Coilpax         All photos copyright John Mills, last updated 27 Dec 2009 The Valve Coilpax was developed to meet a demand for high performance tuners for use as front ends in communications receivers. They possessed a high degree of sensitivity for the time (typically 1uV for 15dB S/N ratio) and good selectivity due to the use of the High Q Stabcoils used in them. They offer a high and low impedance IF output at 1.610MHz. The high sensitivity RF stage uses a high slope frame grid valve type EF183, connected in a Miller compensating circuit, followed by an ECH81 triode heptode frequency changer, using oscillator circuits giving optimum mixing conductance on each waveband without any pulling, each oscillator coil not in use being shorted out. Two models were available, a GC version covering from BC 550Khz - 1.5Mhz and 5 SW bands from 1.7Mhz to 30Mhz. The QP version covered the six hambands of the time, 160m / 80m / 40m / 20m / 15m and 10m. To view a full data sheet courtesy of David G4AKY click HERE. Thanks go to John Hobin G3XIX for his help on providing the circuit of the GC166 GC166 General Coverage QP166 Ham Band Click the images below for larger versions of the circuit diagrams: