HERESY ... My CT-100 Color TV TUNER

[dtvmcdonald]

I looked at all my normal test patterns and test pictures, and a couple of whole
(and colorful!) vacation slide shows (played on a Sony BluRay player).
I also watched Adventures of Robin Hood and The Hobbit I and some live
shows. Results are all near perfect, and better than a real CT-100 on its CRT
because of perfect DC restoration.

A schematic of the converter is attached. It looks and is trivial, but took quite a bit
of work to get all the levels (both voltage and bias current) working right. It uses
a 12-15 volt wall-wart. Its intended for 75 ohm loads. Note that I'm using 1 watt
film resistors for the 1 meg ones. The capacitance of these matters a very lot ...
thus, the trimmers.

http://www.videokarma.org/attachment...1&d=1557588331

[dtvmcdonald]

After a bit of experimentation with a new type color test pattern, I've
decided that the original RCA decision to use unequal bandwidths was
just plain stupid, to the eye. It would have been better to use the
same bandwidth for I as for Q. This was much easier to see on my new
and much brighter display.

My modulator provides equal bandwidth color, as does the DVD player.
All that's needed is to unplug the Q demodulator and apply two color squares, Q and -Q (green/magenta), touching horiaontally. Above I is black, below it, white.
Above -I is white, below it, black. The amount of feedthrough from the Q
into I looks unnoticeable, and in fact is unnoticeable on program material,
especially compared to the blur of Q with narrow bandwidth.

For the CT-100 this would, however, require an additional triode section
in order to make the Q amplifier circuit the exact same as I. I.e., more $.
Later sets of course used cheaper demods, but they would still look lots better, just so long as they were broadband. Compensation in the $ department: a much shorter needed delay line for I.

I just love playing with things like this!

[init4fun]

Originally Posted by dtvmcdonald

....I just love playing with things like this!

I'm surprised no one has commented on your work yet , but I for one am impressed with the engineering you've applied to this and think it's just great ! To see good old fashioned electronic experimentation like this is one of my reasons for hanging around here at VK .

PS , In my opinion it's only Heresy if you can't put the TV back to it's original condition when your done , since your mods aren't irreversible I see no reason for the torches & pitchforks