Where Is The Tint Control?

[Tom9589]

I enjoy looking at old TV schematics, in particular the very first color TV schematics. It's interesting to see how circuit designers accomplish processing the signals.

I particularly like to see how the designers adjust the tint. Sometimes it's a pot; sometimes it's a variable capacitor. Sometimes it even looks like an inductor and capacitor combined.

That said, I was looking at the schematic for the first Admiral color TV, model C1617, on the schematic in the Early Television Foundation's technical information and didn't see any control labeled tint or hue. Where is it? Is it C507 in the plate circuit of V502A?

Curious minds want to know.

[old_tv_nut]

This is the first time I've looked at this set's schematic.
It has a crystal ringing circuit rather than a phase-locked loop, hence the need for a 3.58 amplifier and limiter. There are many tuned circuits that could affect the tint. I'd guess these were aligned as close to peak response as possible and then C507 was the final factory phase adjustment. It appears to me that there was no customer tint control, unless there was a mechanical shaft that brought the C507 adjustment to the outside.

Has anyone seen one of these in person to say?

By the way, showing the crystal as a diode symbol is a mistake.

[Tom9589]

Take a closer look at the crystal symbol on higher magnification. It's three parallel lines with the center one being a little bit shorter than the outer two lines. No arrow symbol here. Look at CR301 and CR301, the video and sound detectors. They have the typical arrow pointing toward the cathode in additional to a + symbol.

I worked for Scientific-Atlanta in the 1970s and we used CR for all diodes and XTAL for crystal designations.

[old_tv_nut]

Originally Posted by Tom9589

Take a closer look at the crystal symbol on higher magnification. It's three parallel lines with the center one being a little bit shorter than the outer two lines...

Thanks - had to really blow it up to see it on my laptop.

I see a resistor spec I'm not familiar with. The video ouptuts have plate resistors marked 10% NIT. What is NIT?

One thing you can say about this chassis is there was no attempt to reduce parts count.

[old_tv_nut]

NI might be non-inductive, but don't know what the T would stand for.

[Yamamaya42]

Technology perhaps? :O

no way to know after all these years what they meant. :/

[Tom9589]

My bet is that it stands for Non-Inductive Technology. Sprague marketed a series of resistors designated NIT. The exact series had the power dissipation before the NIT. I.e., a Sprague Kool Ohm 10 NIT resistor was a 10 watt non-inductive resistor.

In the circuit for the Admiral, these resistors are in series with inductors so it is likely that the circuit designer didn't want any additional unknown amount of inductance added by the wirewound resistor.

[Tom9589]

It would be great if we could identify someone who owns one of these TVs. Just open the door on the front of the TV and see if there is a control labeled tint or hue.

[Tom9589]

There definitely a tint control. I was looking at an article on ETF about the C-1617A and it showed the front panel controls. There are four controls between the volume/contrast control and the tuner. The one closest to the volume control is labeled "Color Fidelity". A picture of the front chassis shows this control is not a pot. It has a phenolic strip which supports an aluminum shaft which probably goes to a variable capacitor, perhaps C507. The "Color Intensity" control is located in the lower, lefthand corner, next to the volume control. This control is definitely a pot which agrees with the schematic (R409).

[Yamamaya42]

Perhaps that TV is from...

https://www.youtube.com/watch?v=8CtjhWhw2I8

[Tom9589]

It's also interesting to note that two of the first color TVs, the GE 15CL100 and the Westinghouse HK840CK15, do not have front panel mounted tint controls. The GE had a screwdriver adjusted variable capacitor on the back chassis and the Westinghouse had a flexible shaft mounted on the rear of the set adjusting a transformer core. I think all future sets had a consumer adjustable tint control on the front panel.

[old_tv_nut]

Originally Posted by Tom9589

My bet is that it stands for Non-Inductive Technology. Sprague marketed a series of resistors designated NIT. The exact series had the power dissipation before the NIT. I.e., a Sprague Kool Ohm 10 NIT resistor was a 10 watt non-inductive resistor.

In the circuit for the Admiral, these resistors are in series with inductors so it is likely that the circuit designer didn't want any additional unknown amount of inductance added by the wirewound resistor.

Aha! "Sprague" is what was needed for the search. There are some salvaged Sprague NIT resistors in a current listing on ebay marked as Sprague KOOLOHM 10 NIT.

[dtvmcdonald]

I do think its interesting to note that my CT-100 never, ever, needs a tint control
adjustment. Sometimes it does need a minor color level adjustment. This is especially true if one uses different channels on it. But set even that and "forget" is just OK if the fine tuning is right. But I aligned the tuner very very carefully on every channel, 2-13 and 39.

[trinescope]

The 15" Westinghouse color circuits are also pretty stable, and that one doesn't use a crystal oscillator, it's closer to a horizontal AFC circuit. I still believe the tint problems were more on the transmitter side, especially when network feeds or videotape was involved.

[Tom9589]

I've often wondered why color TV manufacturers didn't use the system similar to Westinghouse. Was it to eliminate yet another control (color hold) for the customer to mis-adjust?

I wonder how the PAL and SECAM systems handled the color subcarrier oscillator? Crystal controlled, I would think.