Happy Easter - CTC-5
 

Ukrainian/Polish Easter eggs on the old beast...

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Sweet RCA roundie next to a Zenith console, hardwood floors just like at great grandma's place. Very nice

gorgeous set :banana:

:thmbsp:

Nice color!

Yes what a gorgeous picture! Bet most CTC-5s weren't adjusted that well! lol

With the relatively poor video response of the CTC-5 chassis, I've learned that the right font size combined with a black outline makes a huge difference in the readability and therefore apparent sharpness. The black outline in particular makes a much greater improvement than I would have guessed.

Here's a look at the result right out of the camera without adjusting the highlights, shadows, and white balance (and fixing the camera tilt).

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Very cool Wayne.

Wayne,
Can you explain further specifically what you mean by "poor video response"?
Terry

I can't speak for the CTC-5 specifically but all of the later RCA roundies I remember were quite sharp despite the frosted faceplate.

A very nice picture. A trophy indeed!

If you look at a resolution test pattern or multiburst, you can see that the video response rolls off well before 3 MHz. I don't know how much is contributed by the video amps and how much by the delay line, but the circuit doesn't even have or need an explicit 3.58 MHz trap. It makes broadcast pictures be more or less VHS equivalent. This is further smeared by the low high voltage in this set, resulting in poor spot size.

I wonder if it may be an video IF alignment problem? The luma response is no different than the deluxe model.
My VIF test is while viewing the resolution chart, to simply rotate the fine tuning control and see if the resolution markedly improves as the video carrier descends the nyquist slope. It could be the video carrier is sitting above the 50% point.

I found in my CTC5 the RCA or phono connector which attaches the IF coax from the main chassis to the tuner, if dirty, will move the carrier to high.

Nope, I did a full alignment after restoring it. The IF is OK, also verified by the fact that the chroma response is OK and there are no color problems. So, there is full-bandwidth video at the detector, but the video section doesn't pass it. If it had full video bandwidth and an explicit chroma trap like the better chassis and every set afterwards, it wouldn't be so bad. As it is, you can't even see dot crawl on vertical edges.

This Super chassis is full of questionable cost cutting attempts. RCA learned their lesson that it wasn't worth it and never sold a low grade color chassis series simultaneously with a good one again.

Another example, it really needs the audio carrier amp/limiter stage that the better chassis has. If you tune the audio trap dead-on in this chassis, you practically lose audio. It has to be tweaked a bit off to get acceptable volume, hopefully without introducing 920 kHz beats in the picture.

I have reflected upon what you have said. Even on the deluxe, I have been concerned at the lack of dot crawl implying that the RCA engineers expressly rolled off the luma response before 3.58MHz. On the two later sets I have, the RCA CTC-11 and Zenith 24NC31Z, the dot crawl is more apparent. I would be curious if the other CTC5 custodians of both the Super and Deluxe see the same.

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?

As for the added sound IF stage, I agree there is added benefit. To me it imples the added sufficient signal at the ratio detector to improve limiting and remove AM ingress. Certainlt the CTC-5 Deluxe has the best intercarrier sound compared to other sets I have compared of the era.

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.

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.

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.

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.