View Full Version : Hue Control On GE 15CL100


Tom9589
10-29-2016, 12:18 PM
After looking at the schematic on the 15CL100, I noticed that the Hue control is actually mounted on the rear chassis and looks to be a screwdriver adjust. I know that GE uses a different 3.58 MHz oscillator than RCA and the others, but is the GE circuit stable enough to satisfy the consumers or did GE underestimate the need to periodically adjust the hue?

Electronic M
10-29-2016, 01:17 PM
GE's circuit is a resonator not an oscillator. It works like a 3.58Mc tuning fork that gets struck each chroma sync burst and will hold the note for multiple bursts should any be missing.

However the chroma oscillator is not something that typically drifts in a way that requires the hue control to need adjustment....Back then broadcast equipment setup was subjective and prone to drift, and network feeds and some reception conditions were prone to distort the color signal into needing hue correction....It was not a good choice put that control on the back IMO.

old_tv_nut
10-29-2016, 01:35 PM
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.

benman94
10-29-2016, 03:04 PM
I wonder if, under real world conditions, the GE's susceptibility to noise would have even mattered?
It couldn't have performed too poorly, because GE used the circuit in the Porta-Color, which they built for just shy of an eternity...

old_tv_nut
10-29-2016, 07:50 PM
I wonder if, under real world conditions, the GE's susceptibility to noise would have even mattered?
It couldn't have performed too poorly, because GE used the circuit in the Porta-Color, which they built for just shy of an eternity...

It would only matter if the hue streaking noise showed up before the luminance noise was visible - not likely. It's the kind of thing that could show up in comparison of two large screen sets, but is probably not critical.

benman94
10-29-2016, 09:25 PM
In the case of the 15CL100, the coarse shadow mask, coupled with the tiny screen would have made the whole issue moot.
In fact, I'm willing to bet that one would find a 15CL100 preferable in a side by side test with the CT-100. The CT-100, for all of its advantages on paper (IQ demod, the PLL local chroma oscillator, better NF in the front end, etc) has fatal flaws in HV stability and focus voltage regulation.
I noticed at the ETF museum that the technically inferior Westinghouse H840CK15 is more pleasing to watch due to the better HV and focus sections.

miniman82
10-30-2016, 11:16 AM
The issues with HV stability in the CT-100 are easily solvable, I did some circuit mods to mine and it now performs as well as any later roundie.

benman94
10-30-2016, 11:27 AM
If you feel like hot-rodding a set, then sure, more power to you. I prefer to restore my sets to the circuitry it left the factory with. A stock CT-100 is a dog.

dieseljeep
10-30-2016, 11:29 AM
I wonder if, under real world conditions, the GE's susceptibility to noise would have even mattered?
It couldn't have performed too poorly, because GE used the circuit in the Porta-Color, which they built for just shy of an eternity...
If you look into any of the GE designed color sets, you'll find some form of the chrystal-ringer type color circuit. The CB types, KC,KD,KE etc.

old_coot88
10-30-2016, 12:49 PM
If you look into any of the GE designed color sets, you'll find some form of the chrystal-ringer type color circuit. The CB types, KC,KD,KE etc.
One iteration even uses a NE-2 neon bulb in the burst gate circuit. We had one in the shop with no color sync. Replacing the neon bulb cured it, even tho the original bulb was lighting normally.

GE was not our house brand, but we did service quite a few of them. But dang if I can remember one not having a user-accessable tint control of some kind. Lack of a tint control woulda certainly been noteworthy.

dieseljeep
10-30-2016, 01:03 PM
One iteration even uses a NE-2 neon bulb in the burst gate circuit. We had one in the shop with no color sync. Replacing the neon bulb cured it, even tho the original bulb was lighting normally.

GE was not our house brand, but we did service quite a few of them. But dang if I can remember one not having a user-accessable tint control of some kind. Lack of a tint control woulda certainly been noteworthy.

I remember seeing one model that used a compression trimmer with a shaft on it as the tint control. :scratch2: