Westinghouse H-223 restoration

[old_tv_nut]

The other way to adjust contrast would be with a variable resistor in the cathode of the video output. But here they needed a full AC bypass (1000 microfarads) to make the video output have enough gain at maximum contrast - so varying the cathode resistor would only change the DC bias and not affect the contrast significantly. So why not have a variable cathode resistor that goes to zero for max contrast? Because it would result in too much sensitivity of bias to video output tube variations.

How about varying the gain of the video output by varying the bias? The problem is that varying gain by changing tube bias only works well when the signal swing is relatively small compared to the bias voltage, as is the case in IF AGC or color level control based on burst level. If the signal itself is large, it runs from the low-gain region of the tube characteristic to the high gain region, so resulting in differential gain, which means non-linear amplification.

[bandersen]

I finally finished this set last week. Here are some final photos of it assembled and playing well. The controls take some getting used to, but once it's dialed in, the performance is quite good.

What a strange set

[kvflyer]

In a word, "Nice".