CTC-5 Westcott restoration

[old_tv_nut]

Hue (Tint) drift can be due to one of the many cost cutting experiments in the CTC-5 Super chassis. They used burst injection to lock the local oscillator, rather than a phase-locked loop (PLL) with a phase detector and reactance tube. A PLL (as used in the Deluxe chassis and all subsequent chassis) can drive the static phase offset near to zero if it has sufficient loop gain, but the injection locked oscillator is more at the mercy of the oscillator drift with temperature, depending on the "Q" of the circuit and the injection level. So, increasing the burst injection level may improve things.

Years later, Norm Parker at Motorola analyzed the requirements for an injection lock circuit to perform as well as a PLL, and it was successfully used in some Motorola designs.