[old_tv_nut]

There were some Motorola tube color sets (TS-914,918,921)that had three color controls, the third one affecting red/blue DC balance. The way it arose was that they used a single split-pentode tube (6LE8) for the color oscillator/demodulator section.

This tube was a color oscillator operating between the cathode and grid1. This constituted an "electron-coupled oscillator", meaning that the signal was coupled to the plate by the elctron flow, but the plate circuit itself was not part of the oscillator. They injection-locked this oscillator to the burst, so no phase detector was required.

The chroma signal was phase split by 90 degrees and then fed into dual screen grids, resulting in demodulated R-Y and B-Y coming off the dual plates. G-Y came off the single common screen grid! The G-Y was a bit weak for correct colors - greens tended to be desaturated and run toward brown or blue.

Since the color difference signals were DC coupled to the CRT grids, imbalance in the tube's current split would run the picture toward sepia or blue-tone shadows. The more expensive sets had the third control, which adjusted the red/blue DC balance. The really cheap sets just used fixed resistors.

They called this circuit the "SODPIL" - "self oscillating demodulating phase injection lock".