Merry CTC-5 Christmas 2020

[old_tv_nut]

If Thanksgiving has gone, can Christmas be far behind?

This year's presents include two Christmas ball scenes from "Meet Me In St. Louis;" Charlie Brown; and Coca-Cola's Santa.

https://www.flickr.com/photos/old_tv...57717150208857

[JohnCT]

Nice!

[bluenorm]

this hobby of ours is very colorful.

[Penthode]

Wayne,

I have been working on my CTC 5 and have a few questions. I was earlier plagued by bad CRT tracking which made it difficult to get a good greyscale. On my B&K 467 CRT tester, the 21AXP22A red gun emission was poor. It had been like that since I picked up this set seven years ago.

I was reluctant to rejuvenate the gun as I felt some emission was better than none. I however last weekend took the gamble and gave it a good blast and low and behold it woke up! The CRT tracks well, the emission tests good and importantly I now can get a consistent greyscale.

The only thing now is the picture is dim! I have a 1961 CTC-11 with a 70's CRT replacement and it is pretty bright.

What is the condition of your 21AXP22A? And how to you find the relative brightness say compared to the all glass CRT you had in your CTC 5 before the 21AXP22A?

Curious Terry

[old_tv_nut]

The set has always been dim. It was pretty dim with the glass CRT and is dimmer now with the 21AXP22A. However, I feel it may have drifted dimmer with time and may need some TLC to perk it up a bit (but not expecting miracles.)

Besides all the other low-performance issues with this chassis, insufficient luma drive seems to be one. When I have attempted to increase the video level with AGC adjustment, I reach a point where the AGC locks up after changing channels and have to back it off. (I don't recall for sure, but I think this is mentioned in the service info).
The set has aways had way more chroma demod output capability (CRT grids) than is needed to match the cathode drive for proper color saturation.

In making the photos, I noticed that the stills from the adapter on channel 3 were brighter than the movies played from a DVD player into the UHF modulator (a little Chinese-made unit). Not sure if the UHF modulator is undermodulating a bit or what.

I am thinking about retubing the video section, as I definitely have noted before that the video output amplitude in most tube sets is dependent on the gain of the final output tube. In the '67 Magnavox I had, I bought a number of video output tubes and tried them one by one until I found the strongest. It made a big difference, with the CRT looking tired to looking brand new.

I also have noticed in the past that the set seems to be crazy sensitive to replacement of IF tubes, some tubes apparently producing some oscillation or something that totally messes up the picture. Never did figure that out, just substituted tubes until I got a set that works. This, of course, could have some relation to the AGC range.

[old_tv_nut]

Forgot to say: the 21AX is a GE branded rebuild and tests excellent on all 3 guns.

[Popester]

Wayne, where did you get the decorative Christmas tree on top of the tv? Reminds me of one my grandmother had. Hers had the tree fit over a low wattage standard size incandescent bulb. I believe it was a 40 watt. Your pictures are very nice and bring back nice memories. Thank you for that.

[etype2]

Very pleasant nostalgic feeling. :-)

[Yamamaya42]

Originally Posted by Popester

Wayne, where did you get the decorative Christmas tree on top of the tv? Reminds me of one my grandmother had. Hers had the tree fit over a low wattage standard size incandescent bulb. I believe it was a 40 watt. Your pictures are very nice and bring back nice memories. Thank you for that.

40 watts?
Something like that would be warm enough to be a food-warmer!
How about a 7 watt nightlight bulb?

I will try to post more on this sat,

[Penthode]

Your comments are interesting as I am observing the same with the luma drive in my CTC5N or the deluxe chassis. I have noticed white crushing which I had earlier attributed to the CRT. It is a uniform crushing of white highlights. But if it was the CRT, would I have expected a differential crushing which would reveal a color cast depending upon color primary efficiencies? Instead I see a relative uniform white crush.

It is interesting the older design of the CTC5 employing background controls (essentially gun DC brightness shifters) and screen controls makes for challenging effort in getting the guns to track. I discovered in the book "Colour Television" by Carnt and Townsend (published 1961) that they make specific reference to the CTC5 design with the deluxe chassis X-Z demodulator. On page 244 the authors discuss that the X Z vectors are chosen so that the output of the (R'-Y), 0.8(G'-Y) and 0.6(B'-Y) match the phosphor efficiency drive ratios. I see that both the Super and Deluxe chassis share the same luma amplifier circuit even though the Super has R'-Y / G'-Y demodulation. The 'Y signal division to match these ratios are in the plate circuit of the 12BY7 video output tube. E.g. the two 910 ohm resistors in the divider chain. A simple voltage divider calculation reveals 1.0 Red, 0.8 Green and 0.6 Blue.

I mention this because later designs dispensed with background control by virtue of matching as closely as possible the the DC levels applied to the CRT cathodes and the introduction of gain controls to offset the variability of phosphor efficiency differences most likely with aging of the CRT.

To get the CTC5 to track over the full range of brightness control setting, I found that there is a range of interaction between the background and screen adjustment which may be taken advantage of to match gun- phosphor efficiencies. Following the procedure with color gain minimum to initially preset the background controls, the screen controls are adjusted at a near minimum bright control setting for greys near black. Advancing the brightness, if there is a color cast in the whites of say green, return to minimum brightness slightly reduce the green screen and advance green background to ensure grey near black and then advance the brightness and look again at the whites. In other words, the lowering the screen voltage on a particular gun reduces the guns gain slightly to help facilitate good tracking.

I have gone on to explain this at length to show the effort I have expended to get the set to produce a better picture. The problem remains of a relatively dim picture (looks fine in a darkened room). But if you were to advance the contrast and brightness, two things are noticable: first the whites tend to crush and second the DC level reference becomes widely variable. That is the black level shifts all over the place with changing luminance. To me this suggests a problem in the Y amplifier.

Your thoughts?

It is also reassuring that you said the picture was perhaps a little less dim with the later CRT!

[old_tv_nut]

"the variability of phosphor efficiency differences most likely with aging of the CRT"
I don't believe the phosphor aging was so much a problem as the initial efficiency of different phosphor batches.

If I saw white crushing, the first thing I would check is the video output plate waveform, to see if the bias/tracking set up had inadvertently walked me toward biasing the video output amp towards saturation (low plate voltage), crushing the whites there.

[old_tv_nut]

Originally Posted by Popester

Wayne, where did you get the decorative Christmas tree on top of the tv? Reminds me of one my grandmother had. Hers had the tree fit over a low wattage standard size incandescent bulb. I believe it was a 40 watt. Your pictures are very nice and bring back nice memories. Thank you for that.

The ceramic tree was an art project my Godmother made one year (or so I was told). She gave them out to various friends and relatives. Not sure how much of the project was premade and how much of it she did. The illumination is a clear bulb nightlight bulb of only a few watts. Some years back I lost a few of the colored jewels and found they could still be bought, but it took me a year to get them because the craft store would get a small shipment around November and they would sell out. So, I had to start calling them weekly the next November so I could snatch up a bag. Now you can find them on line.

[DavGoodlin]

The ceramic tree my grandma had is still in use here, it had a C-7 candelabra single lamp and flat base with a twist switch on end.

Considering the subject of this thread, its funny that my grandma had a CTC5 but it was a special, Aldrich model, not the "good one" seen above. She always unplugged it in frustration, in wait for service contract fellas to come out from "Fact'ry service" in town just to re-set color controls, usually after she messed it up after changing channels and trying for green grass, blue sky or some other poor reference! So I never saw it work, when I was 8 she traded it for a Chromacolor -LMAO hence 45 years of fascination with early color.

When I get one of my "new vistas" working, Ill put her tree on top just like Wayne did

[Yamamaya42]

Merry Christmas CTC-16XL version!

https://i.imgur.com/M29iwkQ.jpg

did the best I could with the crappy cell cam.

and YES, I have 2 of those trees! so i DO know them!

the one on the set was made by my mom, the one to the right of it was made by my grandmother.

[old_tv_nut]

If you look at the Coca Cola Santa pic, you can see that the white field purity is noticeably imperfect on the 21AXP22A. Convergence is also a bit off. I wonder if it was better before the tube was rebuilt. The replacement gun may have been rotated slightly.

The all glass tube had much better purity and near perfect convergence as well.

White field purity problems were eventually solved by black matrix "negative guard band" tubes.