Westinghouse K840CK15 Restoration

[Penthode]

Originally Posted by dtvmcdonald

On a properly adjusted CT-100, with all the responses (RF, IF, color amp, and the I and Q filters) set up properly, with the infamous bad white peaking coils properly replaced (not easy! ... the specified replacements are wayyyy off) the difference in I and Q colors is not just obvious, its blatant. The screen resolution is much better than the I bandwidth. See the pictures of test patterns I posted years ago, some using exactly correct generator bandwidths.

At times the CT100 at ETF has been good enough.

As I have said before, for just one channel the CT-100 has 81 different adjustments. They all need to be right. This takes either love or paranoia, or both.
My set has the RF for channels 3, 4, 7, 10, 12, and 39 set with love. Other
VHFs are just OK.

I too battled through the process of ensuring the I, Q and Y responses were okay. Recall I made my own peaking coils or modified others to secure proper Y, I and Q responses. In addition I went through the demodulator operations and I checked the matrix resistors and settings and the RF IF response. I checked each VHF channel to confirm response. Comparing the chroma resolution and colour gamut with my other sets, the CT100 does have a sharper picture with better color. I see saturated deep yellows on the set which my friends say is quite remarkable.

Fotrunately the 15GP22 is very much alive but despite that tends to be dim. I have the chassis of the CT100 out on the bench right now as I prepare to construct and install my vertical convergence transformer replacement.

FYI: Yesterday I identified the AGC problem which had plagued me eg the tendency to overload on strong signals. I traced it to the resistive divider feeding the video amplifier screen. The lower end of the divider opened, raising the screen voltage. This in turn forced the video amplifier to conduct more heavily and lowered its plate voltage. The plate of the video amplifier is DC coupled the the 1/2 6AN8 horizontal sync separator which is dc cathode coupled the the grid of the other 1/2 6AN8 AGC keyer. the reduced coupled dc level to the AGC keyer grid inhibits proper agc keying. Replacing the video amp screen resistor restores the the dc level to the agc keyer and the CT100 no longer has the overload problem!

I apologize for the digression. When I have finished with the convergence fix, I plan to spend more time analysing the color perfomance.