CTC-7: Convergence, Convergence, Convergence - Videokarma.org TV - Video

jbeary · #1 08-12-2006, 10:52 PM

Hello All,

Can anyone let me know how come I can’t ever get a perfectly round dot from my dot generator? It’s not the dot generator because it works fine on the new TV which is perfectly converged… Because I can’t get a good dot, I can never get really good convergence and it’s making me crazy.

Could this be caused by having the elements out of whack? Can anyone post a diagram or pics for a CTC-7 neck; maybe with some measurements just to make sure? I get really good purity, but each dot is a different oblong shape. And while I can more or less line them up, the convergence is always off on one side of the screen or the other toward the end of the process.

I’m hooking up the generator through the tuner but no matter how I tune the fine tuning; the dot shape remains the same. Should I be going straight into the video signal to eliminate this? If so, can some one please let me know how to do that on a CTC-7 chassis with that horizontial trigger thingy?

THANK YOU ALL in advance for your help.

Jeff

***Eric H*** · #2 08-13-2006, 12:16 AM

Hi Jeff, I don't know about the dot shape but I seem to remember convergence problems on these sets being caused by a bad Selenium rectifier on the convergence board? Could be wrong, someone please correct me.

If you don't already have one there is a factory service manual for this model posted here: http://www.vintagetvsets.com/schem/ctc7-small.pdf (right click and save or you'll be stuck for a while, 8 meg file)
It has all the info for setup.

Eric

kx250rider · #3 08-13-2006, 01:11 AM

Typically the dots aren't round, due to various SLIGHT tuner and IF problems, and also due to slightly weak CRT or poor video response. Try turning the contrast way down and see if they get more circular. Also, if the TV focus is off, it will malform the dots. But no matter what shape, you can still use the dots for convergence purposes. They just need to be sharp enough.

As far as placement of the components on the neck, you need to refer to a diagram. I could try to explain, but a printed diagram is better. I'm not sure what effect on the generator dots mis-installed neck components might cause, but I can say for sure that those things need to be right in order to get convergence and purity. Any of the RCA factory manuals, or the Color Pict-O-Guide, or any early color TV repair textbook will have a diagram.

Charles

Chad Hauris · #4 08-13-2006, 01:29 AM

Also make sure the vertical linearity is good...if you have weak tubes or caps in the vert section and have the vert height control at maximum you may be getting distortion of the vertical waveform.
Make sure too there is not a pot on the convergnce board which has an open segment in the resistance element.

jbeary · #5 08-13-2006, 11:43 AM

Hello Guys,

Thanks and I'll try all this stuff. I never did replace the selenium rectifier on the convergance board, so I'll try that too. Thanks so much for pointing me to a factory service manual. That's better than the Sams I have for sure!

Will let you guys know the results.

Reards,
Jeff

vintagecollect · #6 08-13-2006, 06:30 PM

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reeferman · #7 08-13-2006, 09:43 PM

Jeff,

Don't be to hard on yourself expecting perfect convergence because it won't happen. This was the first roundie to have the "modern" convergence board.

I doubt the selenium is bad. I tried putting in the more modern style in (like from a CTC-16) but not once did it make a difference.

To get a better dot/crosshatch adjust the brightness along with the contrast. Try injecting a video signal vs. running it through the antenna terminals

Have patience and enjoy. Good luck.

Phil

Chad Hauris · #8 08-13-2006, 09:59 PM

The round sets are capable of as good of convergence as modern sets if set up right...the convergence is actually easier to set up on the rounds rather than the rectangular delta gun sets.

reeferman · #9 08-13-2006, 10:14 PM

Chad,

I agree very much with what you say! All I'm saying to Jeff is not to expect the set to perform like it did 40 yrs ago

Phil

blue_lateral · #10 08-14-2006, 05:44 PM

You really need a picture from one of the books, but I'll try.

The yoke goes anywhere for now. there are pole pieces on each gun. The convergence electromagnets go over these, not the sliding magnets. There is probably a coating on the neck blocking your view. Try to look up in there and see them. They might be under the pink stuff inside the neck (if you have it). In any event, look forward and try to see them. Center the convergence yoke over them, blue on top. They are the same thickness as the convergence yoke, so if you can see one edge of the pole pieces, you can figure it out.

Next comes the purity rings. They might have more plastic on one side than the other. I forget which way, but you can sort of tell because the rings I think. The extra plastic probably goes forward. The rings go over a gap between the elements of the electron guns. This is going to put them really, really close to the static convergence magnets.

The blue lateral comes next. there is a pole piece on top of the blue gun for this. The magnet is centered front to rear over this pole piece, but twisted to about the 2 o'clock position on the neck. If you have the blue lateral that turns, the short part thats through the bracket is what goes at 2 o'clock. If you have the bar magnet, the magnet goes at 2 o'clock. If you have the one with a little bump of a magnet strapped directly to the neck, start out at 2 o'clock, and adjust by changing the clock position.

If you have something in the wrong way, like the purity magnets, you probably cant get blue lateral forward enough to be over the pole piece. This stuff is really crammed together when its put on there by the book.

The blue pole piece is at focus voltage (6kv) with the set running, and the blue lateral is usually grounded. If you can maximize the distance between the blue pole piece and the grounded bracket by adjusting clock position, It's probably a good Idea. Probably only possible on the bar magnet kind.

All the best,

John

jbeary · #11 08-14-2006, 06:11 PM

Thank you all for trying to help me. I'm going to post a picture of what I currently have because it sounds like I have everything in the correct spot but I still want to make sure. I look forward to someone telling me that I have it all wrong but so far it all seems right. I just can't see the pole pieces inside the neck and this is what I feel is throwing me. I've tested the position of the convergance yoke by sliding it back and forth as well as side to side and everything nets a different result. Of course, I'm looking for the best one

6K on the lateral magnet band??? YOWAZA! I hope that I don't lose that ground. I better check the solder joint on that thing because when this sucker shocks you, it does it real good.

Also, if anyone wants to chime in on injecting the video into the 2nd IF amp, please do.

THANKS AGAIN GUYS!

blue_lateral · #12 08-14-2006, 08:07 PM

Quote:

Originally Posted by jbeary

6K on the lateral magnet band??? YOWAZA! I hope that I don't lose that ground. I better check the solder joint on that thing because when this sucker shocks you, it does it real good.

Naw, 6k on the pole piece inside the tube.

It shouldnt arc out because of the vacuum and the glass. The lateral itself is usually grounded.

John

reeferman · #13 08-14-2006, 06:15 PM

John,

I can PDF some stuff to you from the RCA Service Manual. You can get good, but I doubt perfect is achieveable. There are just to many dynamics involved (like the shadow mask). Play with the set, experiment, gain some experience, and have some fun.

Phil

Whirled One · #14 08-14-2006, 07:52 PM

Quote:

Originally Posted by reeferman

You can get good, but I doubt perfect is achieveable. There are just to many dynamics involved (like the shadow mask). Play with the set, experiment, gain some experience, and have some fun.

I gotta agree with Phil here-- I wouldn't expect to get absolutely *perfect* convergence on an early color set no matter what you do or what you replace. Try to get it as good as you can, but don't expect perfection. This was a common comment/criticism even in _Consumer Reports_ reviews on color sets through the 50's. Convergence generally improved with each generation though. At least the CTC-7 can't be as tricky in that regard as the CTC-5, which still had a metal-coned CRT and needed those edge purity magnet adjustments, along with DC static convergence that tends to drift according to line voltage. Anyway, have fun, but don't feel bad-- I doubt even the RCA service folks could get these things totally perfect.

roundscreen · #15 08-14-2006, 08:01 PM

Jeff
The round color crt is vary fussy when it comes to magnetic fields in and around the room. Every time I move a set it will change the purity and convergence and I have to realign the crt. I have found when you point the neck of the crt to the south and the screen north [ or neck north, screen south } when doing a alignment it will be easier to get purity and convergence right, But not perfect. {The blue vert lines are the ones I have the most problems with.} Put the set were you are going to watch it, Demagnetize the crt and set. Do purity and center convergence. Then cut off the blue gun {turn down blue screen and drive} and converge the red and green first. Then converge the blue to the red and green. Reeferman is right, You may have play with the set to get the experience. If you get lost , Take a break for a few days and then attack at it again.
Ed