I just checked my 100 here in Wisconsin (Cabinet number 20) and it too is darker below the seam. My other two 100s are in California so I cannot check them for a while but if I recall they too are darker below the seam.

Steve

I never noticed it before but mine is also slightly darker below and beginning at the seam. I have Cabinet #951.

:) Makes me feel better reading that!

This is a great thread. I continue to learn a lot by reading the travails of other collectors. Thanks to everyone involved for making me less ignorant. Some day I may even tackle one of my color sets...

Happy New Year!

-- Dave Sica

Ditto.... I think everyone can say that....

I've been busy refinishing the cabinet for several weeks. In the future, I'll remind myself not to refinish things in the middle of the winter, since the drying time for every step is much longer -- even in our relatively mild California winters. Often had to set the cabinet outside in the sun to move things along!

http://www.videokarma.org/attachment...1&d=1389904925

http://www.videokarma.org/attachment...1&d=1389905245

Overall it came out pretty decent. I'm not sure the color is exactly right, although it's hard to know exactly what the original color was on these.

This was a labor-intensive cabinet restoration, with plywood and veneer repairs in addition to the usual refinishing. I'll give some more details about that below in another post.

Here are some shots of the work in progress:

1. Main cabinet ready to strip (front moulding and speaker grill slats removed):
http://www.videokarma.org/attachment...1&d=1389906434

2. Front moulding and speaker grill slats ready to strip:
http://www.videokarma.org/attachment...1&d=1389906434

Removing the moulding and speaker slats made stripping and sanding much more straightforward. Luckily, they came off easily without any damage.

3. This pesky gap in both of the top front corners caused me a fair amount of grief:
http://www.videokarma.org/attachment...1&d=1389906434

First I tried clamping and gluing. It required so much force to close it up that it simply came apart again after unclamping. I settled on lighter clamping and gluing, which didn't really close up the gap, but would hopefully stabilize it. Then I filled it with wood filler and sanded back. Unfortunately, it still cracked open a little during subsequent finishing steps and required some rework. Came out reasonably OK, but not perfect.

4. Plywood repair for rear foot:
http://www.videokarma.org/attachment...1&d=1389906434

This rear foot was badly damaged, so the original plywood was removed and replaced with new plywood. Although this picture shows some veneer remaining above the new plywood up to the groove, I later removed that as well, and put a single new piece of veneer in place from the bottom of the foot up to the groove, with only a vertical seam against the existing veneer.

5. Rear foot after plywood and veneer repair:
http://www.videokarma.org/attachment...1&d=1389906434

6. Veneer repair for front foot (the plywood was still usable on this foot, with a little wood filler to fill in some missing gaps):
http://www.videokarma.org/attachment...1&d=1389906434

You can also see above that there is substantial wood fill on the front of the front foot. They were badly rounded and beat up from this set being moved (or shall we say "dragged across the pavement by idiots") way too many times over the years.

7. All stripped and ready to stain:
http://www.videokarma.org/attachment...1&d=1389907085

8. Stained and ready to reassemble:
http://www.videokarma.org/attachment...1&d=1389907085

The stain I used was Zar brand "Dark Mahogany" followed by "Cabernet." The Dark Mahogany alone was not sufficiently red, and adding a coat of Cabernet got it to where I wanted it. I like Zar stains because they do not overemphasize the grain, giving a final appearance closer to the original stain + toned lacker used by RCA.

9. Masking in preparation for painting the gold stripe on the front edge of the front moulding:
http://www.videokarma.org/attachment...1&d=1389907085

10. Gold strip painted using Rust-o-leum "Aged Brass" spray paint:
http://www.videokarma.org/attachment...1&d=1389907085

In retrospect, I think "Aged Brass" isn't really dark enough, and I would suggest using "Antique Brass" (a little darker color also available) to get a closer match to the original.

11. Gold stripe done:
http://www.videokarma.org/attachment...1&d=1389907085

Tom,

Looking really good. That one troublesome corner was probably warped and no amount of clamping & gluing would bring it back to true. I wish I had had the knowledge I have now when I refinished my CT-100 years ago. Much warmer here in So. Ca. this winter.

Best,
-Steve D.

Multiple coats of clear finish were applied. After a couple of coats, the following two steps were done.

12. Wall of hole on side of cabinet (for Focus and Convergence controls) painted with very dark brown paint to cover up the grain and plywood structure:
http://www.videokarma.org/attachment...1&d=1389907522

13. Decals (Thanks, Nick!!) were applied:
http://www.videokarma.org/attachment...1&d=1389907522

After more coats of clear finish, with sanding in between, the edges of the decal are almost invisible on the finished cabinet.

So there you have it... That's what's been keeping me busy for a few weeks (in addition to Christmas travel, job, and various radio and TV restoration projects for other folks on the side).

Now I can reassemble things and get back to work finishing up a few remaining electronics issues with the chassis.

Beautiful work Tom! It probably looks pretty close to what it did when it left the RCA factory.

Steve

Looking good!

Today's nit: there should be a small gold dot between OFF and VOLUME. The guy who made my decals accidentally omitted the dot; my refinisher added it back with a fine artist brush and gold paint.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Hi Phil,

I probably won't bother with the gold dot, since I don't even have knobs for my front panel controls! I suspect my CT-100 will be known as "the knobless one." :)

On behalf of a number of people who have benefited from the decals you originally had made, thanks very much for making them available.

This looks really cool.

Just looking at the photos transport me to a time before I was born.

Life was so much simpler when this set was new.

Cabinet is done now, except for the brass frame around the safety glass, which I'm still contemplating what to do with. If I polish it, it's hard to get it back to the right "antique brass" color.

The set is reassembled and working reasonably well. After fixing a problem with the vertical dynamic convergence, I can get the convergence pretty close:

http://www.videokarma.org/attachment...1&d=1390199103

Here's a closeup of the lower left area:

http://www.videokarma.org/attachment...1&d=1390200291

As you can see, the bottom left area is not quite fully converged. The interaction between the vertical and horizontal dynamic convergence controls makes this all rather tricky. The convergence directions in both Sams and the RCA Service Manual offer only limited advice. One thing I notice is that although there are three horizontal convergence adjustments, the directions only mention two. The third, in the high voltage cage (at the top) has a big effect, but I didn't see any instructions on a procedure for adjusting it.

Does anyone have a clear understanding of what each of the three horizontal dynamic convergence adjustments really does? Any tips on further improvement of convergence?

The picture is pretty watchable now, although color tracking is marginal. Although all three guns test very good on my CR-70, the red gun does test a little weaker than the other two, and this becomes very apparent when adjusting the background, drive, and screen controls. The red screen is set at max (about 440 volts on the red screen), the other screens near minimum, the green drive is set at minimum, and no amount of fiddling with everything else can really get the tracking to be excellent.

Here's a screen shot where things look reasonable normal as far as color goes:

http://www.videokarma.org/attachment...1&d=1390199103

You can age polished brass with gun bluing liquid from a sporting goods store. You can also buy proprietary stuff for the same purpose, but I don't know whether that has any real advantage.

I was shown how to do this by a guy with an antique lamp restoration business. The brass should be clean -- as in alcohol-wash clean -- and handled only with forceps until the aging is done. It's easier to do with small pieces that you can dip. For long pieces, I guess you would brush or spray it on. As soon as the brass reaches the desired shade, you wash off the solution.

That convergence looks pretty good. If there are secret tricks for making it perfect, I'd love to learn them. I don't think any of my old color sets has ideal convergence.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

that sets looks as good as it did when brand new!i saw several of these back in the 50s and they never had convergence that close.even new right out of the box!you did a beautiful restoration on this.post more pics

Agreed amazing job on this set! Clearly a labor of love

Trying to obtain "perfect" convergence on these vintage sets will drive you nuts.
You have to know when to walk away.

-Steve D.

Three signs that tell me when the convergence is good enough:

1. After crouching for hours, my back feels like someone stabbed a sword into it.

2. The air is thick with foul language.

3. I hear voices from the other room: "Are you still fiddling with that? We're sitting down to dinner!"

:)

Phil Nelson

Will those little magnetic paper strips help with the corner convergence?

Tom, your work on that CT-100 is fantastic, a real gift to the early television community.

I would not have known that you could disassemble the cabinet and especially the speaker grille that way. Your results give me high hope for improving my own CT-100 in the future.

I've been enjoying watching this set over the past few days, but there was one major shortcoming -- the focus stability. I could adjust the focus for a poor compromise: slightly out of focus for a dark scene, nicely in focus for a medium bright scene, and completely blown-out of focus for a bright scene.

Measurements showed that the problem was not insufficient HV anode voltage regulation, but rather unstable focus voltage. The focus supply is completely unregulated, and unfortunately it seems that the current drawn by the focus grid of the CRT varies quite a bit with scene brightness.

Looking at the circuit, I got the idea of using a high voltage zener diode to stabilize the focus voltage:

http://www.videokarma.org/attachment...1&d=1390445303

I replaced the resistor below the focus pot with a 3000 volt zener. Or more precisely, a string of 15 Z4KE200A 200 volt 1.5 watt zener diodes. Here are a few pictures:

http://www.videokarma.org/attachment...1&d=1390445303

http://www.videokarma.org/attachment...1&d=1390445303

Somewhat to my surprise, this is a fantastic fix. The focus goes from being completely problematic to rock solid. I can turn the brightness and contrast up all the way, to the point the picture looks very bad in other respects, but the focus stays sharp under all circumstances!

Now I realize this isn't really "preservation," but given that I have had the experience of seeing how the set works in its original state, I would say I have experienced that enough, and now I'm ready to watch a set that really works.

Given that my high voltage cage doesn't look particularly original any more because of the big voltage tripler module, this little insertion of a string of small zener diodes is hardly noticeable, and of course is easily reversible.

Great idea!

Genius!

How creative. May I ask what gave you this idea?

Phil Nelson

Well, a zener diode is basically the simplest kind of voltage regulation circuit, quite useful when a fairly limited range of current supply is needed. I was curious how high a voltage one could find in a single zener, and generally found that common ones top out at 200 volts. Since they are quite inexpensive, putting a bunch of them in series is still quite cheap, and they don't take up much space.

I've used zener regulation in battery eliminator power supplies I've built for 1920s radios and later tube-type portable radios, so I'm generally familiar with their usage for this purpose.

The current in the focus circuit is very low, so not much power dissipation is needed. Using 1.5 watt rated diodes is complete overkill, but there was no real cost difference between these are lower power ones, so I went with these.

I also bought some 4 kV rectifier diodes with the idea of putting several in series to replace the 1X2 focus rectifier tube in case that was also needed. But so far, it seems to be fine with the original vacuum tube rectifier, so I'll leave that in there in the interest of keeping as much of the vintage circuitry going as possible.

I've done a little more circuitry modification this evening to improve the color tracking from dark to light. Basically, with the condition my CRT is in (which doesn't seem all that bad on the tester, but does show a weaker red gun compare to the other two), I found that it was not possible to adjust the green and blue drive low enough or the green background high enough, if I had the screen settings about right for good grey level color balance. So I modified the range of all those controls, and now the color tracking from black to white is reasonably decent.

These changes have slightly hurt the dynamic convergence, so I'll go back and see if that can be improved by readjustment now that the other settings seem to be in the right range. In particular, adjustment of the screen voltages seems to impact convergence (and focus) so it's not surprising that convergence will need some touch up.

Adjustable high voltage shunt regulators based on a string of zener diodes combined with a totem pole arrangement of bipolar transistors were fairly common in high end display monitor high voltage power supplies throughout the 80's. They were used for the Focus, G2 and G1 outputs, and could be very tightly regulated if used in conjunction with a feedback loop and error amplifier. If I recall correctly, we used 1N5281 zeners and 2N6517 transistors for the Focus and G2 circuits, and 2N6520 transistors for the G1. I used to design them for a living. Great idea for your CT100!

Does anyone know what the original back cover screws looked like on this set? I've got the original back cover, but it was tacked on with just a few dissimilar screws. I'll get a set of something that looks similar to the originals if I can find out what they were.

Tom,


If you're interested in CT-100 'hot rodding', I dabbled with a few circuit mods that RCA themselves included in later chassis.

For starters the vertical oscillator circuit in the CTC-2 gets its plate voltage directly from the LV power supply, where on later chassis it would come from B+boost. This change was necessary in later sets having larger screen sizes, because with the vertical circuit powered from the LV supply changes in horizontal width would not have any influence on vertical height. The result was that on an overly bright scene which might tend to load the horizontal section (really any situation where the potential of the horizontal circuit changed drastically, such as line fluctuations), horizontal width would tend to shrink while vertical remained largely unchanged. This causes the picture to appear somewhat 'squeezed', much like drawing an image on a rubber band or silly putty and stretching it out. Thus with vertical potential directly tied to horizontal the entire picture size would change in a more or less equal way, rather than losing only width and ending up with funny raster geometry. It's really noticeable with a crosshatch on screen, less objectionable with live images.

I moved the vertical plate supply to B+boost on my chassis and it works quite well, only other thing I had to change was the value of R144 (Sams) to account for the different supply voltage. Picture size now tracks well regardless of picture content, no more stretchy raster. I don't remember what value I ended up with, I just futzed around with different value resistors till I had something that worked well with the range of the height control.

I believe later sets also had the shunt regulator cathode returned to B+boost, rather than B+ or ground. This leads to less voltage across the tube, potentially making it more stable as a circuit but also lessening the stress on it in operation. It's not uncommon for shunt regs to have red plates in operation, but some of them really get hot. Not that 6BD4's are getting scarce or anything, just for the sake of what I will term 'generational improvements' in the chassis. No reason for the CTC-2 to fall behind in other areas, when it was blessed with such great picture quality right?


Lastly, I seem to recall the resistors in the shunt reg control circuit had drifted a lot, leading to no real ability to bring HV into it's proper range. After I replaced the out of spec ones, I could now vary HV into the correct range.

Great looking set, there's room to be much better! :thmbsp:

Thanks for the tips on possible modification of the vertical deflection power supply. I'll keep an eye out for the type of image squeeze you describe, and fix it if it looks like it's a problem. So far I don't see it, so perhaps that happens more with the larger screen sizes of later sets as you describe.

My shunt regulator is working fine, so I won't need to change resistors there. On the other hand, man did this set need a lot of work to get this far. If I was looking for a trial-by-fire set to learn about color TV, this set ended up giving it to me and more. Particularly in the area of alignment it needed many hours of work. And of course all the stuff with the flyback and voltage tripler ended up giving me more education than I necessarily had intended to sign up for!

After making some minor modifications to the adjustment ranges of the various color drive, screen, and background control ranges, I gave the convergence some more attention. I was able to get it much better after figuring out that the position and orientation of the yoke has a pretty big impact on convergence (as well as purity, raster scan linearity, and probably a few more things!). After some careful adjustment of yoke position and observing the interaction with the convergence adjustments, I got it looking reasonably decent:

http://www.videokarma.org/attachment...1&d=1390545223

No problematic areas left in any part of the screen, although there is just a touch of misconvergence on the left. Mainly I wanted to fix the poor convergence I previously had on the bottom, because that is where text banners often appear, and poor convergence really messes up the fine print.

I also found I was able to get the vertical linearity better at the bottom of the screen by replacing the vertical osc/output tube.

I think I *might* actually be "mostly done" with electronic restoration. Color fidelity is by no means outstanding, although I'm not sure how good these sets can really be. I know my CRT red gun is a little weak, and that is certainly making it difficult to get good color tracking from black to white. Also, certain colors like orange are never quite right. Nonetheless, it's quite a lot of fun to watch now. I'm probably overdoing it here, but here are a bunch of screen shots off live over-the-air TV this evening:

http://www.videokarma.org/attachment...1&d=1390545223

http://www.videokarma.org/attachment...1&d=1390545223

http://www.videokarma.org/attachment...1&d=1390545223

http://www.videokarma.org/attachment...1&d=1390545223

http://www.videokarma.org/attachment...1&d=1390545223

With all the work that has gone into aligning, adjusting, etc., I simply can't imagine that the typical TV sales shop was capable of really doing justice to one of these sets when installing in a customer's home. In New York City or Philadelphia, maybe some RCA factory hot shot set up the sets for customers, but in other places I imagine the skill level of the installation techs was mixed at best.

I remember as a kid in the late 60s and early 70s seeing color sets at neighbors' homes that were wildly out of adjustment, and those were sets a lot newer that this that weren't nearly so difficult to adjust. I can only imagine how some of these CT-100s looked in customers' homes in the mid 1950s! Maybe some of you remember those times and can tell me I'm wrong...

that convergence is as good as i ve ever seen.amazing its perfect!set looks great and i applaud your work.if i remember correctly,these sets had a different look as far as color fidelity.afterall,these were among the first color sets and there were many improvements to be made.overall,they had a nice look to them and i actually own one.mine is in climate controlled storage.restored by stan cash back in the 90s,the picture is beautiful.i got it due to the death of original owner.cabinet was restored and flawless.convergence is very good,but not quite as good as yours.that part of the job took stan many hours.he stated it was difficult to get it correct but its looks good.my crt is excellent.these are a wonderful piece of history and glad that another one is in operation.

I've seen customers back in the day who, since it was a color set, would crank the color up all the way.
And BTW, the degree of convergence you've achieved on this set would pass muster on any roundie.

An uncle of mine had one for a few weeks in 1954, this in Ft. Worth TX.
This was a loaner while his mono giant console was being fixed. It looked
just fine in color. In B&W the purity was less than perfect but watchable.
Convergence I remember as no problem.

He liked color so much that when the 21CT55 came out he bought one.
In Ft. Worth we had the big advantage that all local programs
were in color, right from day 1. And there were lots of studio
productions. On the 21CT55 they looked fine too. I've told this story before.
Oh but did I mention he was 1/2 mile from the transmitter?


Doug McDonald

Hey Doug,

I bet your Uncle viewed this station break slide on his new 21CT55 back in late '54.

-Steve D.

Wow, what a nice set. the linearity of that test pattern is superb.. this set is older than my father!
I know the feeling of hearing, 'we're sitting down to dinner!' and all you want to do is just finish the damn thing already. BTW, I've seen CRT sets from the 1990s which had awfully misadjusted convergence. I have battled crt set-up on mostly rectangular sets and it really is a pain.
From one Tom to another, excellent job:thmbsp:

Wow what an accomplishment! Boy I'd love to come see your set in person someday. I believe I work in the same town as you. We might even be working for the same employer. I don't have the ability to collect and restore televisions since all of my time and space is taken up with 35mm movie and projector collecting. I "collect and restore" sets vicariously on this board through reading everyones posts and stories here. Congratulations on your remarkable achievement! -Sean

Well, maybe on the loaner. It was months later that he got the 21 incher.

Doug Mcdonald

Wow looks like you really got her humming!

I'd like to improve the color tracking a little more if I can. What I've noticed is that the color is quite good if the overall scene is dark, but on brighter scenes, the red becomes weak. What is peculiar to me is that the red becomes weaker in a bright scene than it is in a dark scene. For example, if there is some red lettering or a red object on the screen, and the rest of the scene shifts from darker to lighter, the red stuff actually gets dimmer. Likewise, a face that looks normal if the background is dark loses its red content if the background gets lighter, even though the brightness of the face is unchanged.

I'm wondering if there is a problem in my DC restoration circuitry (particularly for red), or if the DC restoration circuitry is having trouble dealing with the difference between the guns in my CRT?

I've got the red screen at max, blue and green screens much lower, and both the blue and green drive below their original minimum settings (resistors modified). The red background with low brightness is too high, even though green and blue background are set at max. In general, the brightness control does not have the correct range -- it basically always needs to be fully clockwise, and still the image is a little dark, although not bad.

Here is the data on the CRT (see pictures below: #1 red, #2 green, #3 blue). All three guns test with very high emission. Key difference is the cutoff bias:

Red cutoff bias: -51.5 V
Green cutoff bias: -66 V
Blue cutoff bias: -67 V

I also checked the screen voltage during the emission test on my CR-70:

Red screen: 259 V
Green screen: 188 V
Blue screen: 225 V

So although all three guns are capable of high emission, there are significant differences between them in terms of bias and screen current/voltage.

Should the set be easily able to handle these differences within normal control ranges?

Any indication of something not quite right in the video amplifiers or DC restoration circuits?

If it's merely a matter of the set not being able to handle the gun differences within normal design range, I'd like to modify things to work better with the CRT in its current state, if I can figure out what would work.

Since many of you have far more experience with color sets than I do, I thought one of you might have some ideas.

i have a cr70 also and with that much emission your crt is NOT the problem. the sencore testers are spot on as far as im concerned. steve