Happy Easter - CTC-5

[dtvmcdonald]

For RCA color sets of that era, the video (Y) response is totally dependant
on the peaking coils.

And if replace one or more, it can make a huge difference!

You see, RCA (and Sams) specify only the nominal inductance.

That's not what determines the frequence response.

What determines it is the parallel resonance frequency of the coil plus
circuit capacitance.

How I got the perfect picture I have on my RCA sets is getting the right
peaking coils. Except for the 6.8 mH coil in the CT-100 "Q" (use 3.3 mH)
the specified values are just fine. When getting coils, rummage through
Mouser and Digikey for the little molded axial coils, shielded is nice, from Bourns, Miller, and API Delavan. Get ones that have resonance frequencies
well above the needed value (e.g. above 7 mHz for Y, above 4 for I, and above 2 for Q or narrowband color). Higher is better. Get some tiny ceramic or
mica caps at 1, 2, 4.7, and 6.8 pf. Parallel the caps with the coils to your taste. Use one of the the test DVDs for NTSC. Don't use a regular scope probe. Use a short (2-5 foot) piece of coax to the regular 1 meg scope input
with a 1 or 2 pF capacitor in series with it right at the point of attachment with the TV.

[Penthode]

Thanks for the response! (Excuse the pun).

It had crossed my mind that the inductance of the peaking coils may have shifted over the years. However my late 1940's RCA sets have very sharp pictures and can resolve the 4MHz test pattern bar. So maybe it was the limit RCA put on the luma response in those early years to conceal the dots.

I have an old Measurements Lab Grid Dip Meter and the application notes include using it to help design the video amp and choice of peaking coils.

Thanks for confirming what had been in the back of my mind for some years that changing the coils can alleviate the narrow luma bandpass.

[old_tv_nut]

Ditto - thanks for the peaking coil comments.

I'm aware of the resonant frequency issue in video circuits. Most of the peaking coils in the Super chassis are in locations where failing open should cause an obvious problem, but not all - specifically thinking of L27 (in SAMS), series coil with the video output grid. I should check it.

[old_coot88]

Originally Posted by Penthode

The added Chroma bandwith on the Deluxe means that you should see more chroma detail. Although the Deluxe uniquely for this one chassis only employed wide band equiband chroma demodulation which implies quadrature crosstalk at the higher chroma frequencies. I wonder if in the end there was really that much added benefit since subsequently RCA never employed the wideband chroma again?

The chroma component of the pic does not require high resolution since it's essentially just "painted onto" the BW component. This simplistic explanation was offered by a factory rep at "RCA School" at the distributor in Phoenix.

[Penthode]

Originally Posted by old_coot88

The chroma component of the pic does not require high resolution since it's essentially just "painted onto" the BW component. This simplistic explanation was offered by a factory rep at "RCA School" at the distributor in Phoenix.

Fine luma detail is independent of the chroma response. However I believe the extension of the chroma bandwidth does allow one to resolve the color of distant eyes as such. In the narrow equiband sets blue eyes would appear black. In other words painting in more color detail with a finer brush.