Another RCA CT-100 discovery B8001599

[Penthode]

Originally Posted by old_tv_nut

Ditto.

I think black level ("Brightness" control) is a tad high in these photos - an easy adjustment. Things like this can happen if you adjust the set with room lights on and then turn them off to take pics or vice versa. If the brightness control is at minimum, it would indicate that CRT bias voltages need some adjustment.

Also want to suggest taking the time to get the camera lined up dead center to avoid perspective distortion.

Blame it on an impatient photographer! I was busy with other things and did not spend sufficient time grabbing snapshots.

To digress a little bit, I am impressed with the setup procedure of the CT100 however. Because the matrixing is external from the CRT and R, G and B are DC restored immediately before the signals are applied to their respective grids, the setup was simple and effective:
1. Set Color Control to minimum. With brightness control maximum and contrast control minimum, adjust screen controls for a barely viable gray raster.
2. With a bright image, adjust blue/ green gain for white highlights.
3. Adjust blue/background controls for gray in low levels.

I found after this adjustment, the resultant brightness range was ample and correct and the grayscale very good.

Further digressing, with good DC restoration I feel I now have a better understanding why later monochrome sets had little or no DC restoration. With blacks firmly clamped, if the CRT limited beam current and/or high voltage supply is not up to reproducing high average picture luminance, picture blooming results.

This and other CT100s I have seen appear very susceptible to this. You may set to haved good overall contrast and brightness on an average picture when a bright overall scene will cause the image to bloom out of focus and disappear. Watching in a darkened room with lowered brightness and contrast is fine.

It is amusing to reflect on a an article I saw in "Wired" regarding the anniversary of the launch of the CT100. It included a republished current (1954) review of the CT100 and the reviewer complained about the soft and fuzzy picture. No doubt in comparison with a bright 21" monochrome set of the same period, the viewing of the CT100 must have been in less than ideal conditions with the brightness and contrast too far advanced!

I am glad therefore I have the opportunity here to reduce rather than increase the brightness (black level).