Video Polarity and Direct Injection

[kf4rca]

What is the polarity at the CRT? Are you looking at the schematic or a scope?
The CRT should be positive. Which means the driver tube input should be negative.
The output of the detector is usually negative, because it is transmitted that way. (Sync is peak power.)
Some of those detector circuits produce 5V of video.

[Electronic M]

Originally Posted by kf4rca

What is the polarity at the CRT? Are you looking at the schematic or a scope?
The CRT should be positive. Which means the driver tube input should be negative.
The output of the detector is usually negative, because it is transmitted that way. (Sync is peak power.)
Some of those detector circuits produce 5V of video.

There is no fixed polarity that MUST be sent to a CRT. The polarity of video you feed a CRT depends on whether it is cathode injected video or grid injected video....Both injection schemes were used back in the day*, and those 2 schemes want the opposite polarity of each other.

*In fact color sets used both at once to effectively mix the color difference and monochrome signals into RGB in the electron gun to save a few signal tubes in the design.

[vts1134]

Originally Posted by kf4rca

What is the polarity at the CRT? Are you looking at the schematic or a scope?
The CRT should be positive. Which means the driver tube input should be negative.
The output of the detector is usually negative, because it is transmitted that way. (Sync is peak power.)
Some of those detector circuits produce 5V of video.

The output of the detector is positive on this set. The video is amplified once and then fed to the grid of the kinescope.