Hue Control On GE 15CL100

[old_tv_nut]

Let's say they were overly optimistic, due to variations in broadcast burst phase.

The GE circuit is a crystal ringing circuit, that is, it does not oscillate. Instead, the crystal is lightly loaded (to keep the Q high) and is shock excited by the burst, after which it continues to resonate through the active line, with gradually decreasing amplitude. The following amplifier and limiter produce a constant-amplitude output to drive the demodulators.

Any circuit that uses a high impedance point tuning with a small variable capacitor will be difficult to bring out to the face of the chassis because the strays will overwhelm it. So, you need to put the cap at the circuit and use a long mechanical shaft.

[EDIT: the schematic shows a shielded cable going to the hue control cap; can someone verify that this allowed it to be mounted on the back?]

The comparison between and oscillator + phase detector circuit (Phase Locked Loop, PLL) and a ringing circuit is:

1) If the ringing circuit Q is high enough, its phase pull vs. frequency drift may be similar to a PLL.

2) A small loop bandwidth in a PLL reduces susceptibility to noise; this is independent of the crystal Q, except that the loop must be wide enough to pull in the oscillator from the extremes of its possible thermal drift.

The ringing circuit will introduce more hue streaking under noisy conditions, depending on its Q and the associated bandwidth of the circuit.