CT-100 S/N B8002601 is Operational

[Tim]

Hi folks. Here are the first pictures from my CT-100. Still need convergence and purity but I do have video. The color lock problem I noticed on the scope reported earlier turned out to be a bad ceramic capacitor in the burst oscilator.

I also lost the 275 volt line during troubleshooting and found that the field Neut. pot protected my newly added fuse. 275ma should not have been a problem for a 30 ohm 3 watt pot. I had it fused at 315ma. I disassembled it and soldered over the break. It has run Ok since then so I am not sure what caused it to fail. I tried to locate a replacement and tapped pots are just not made any more. Hopefully it will continue to function.

I also had a 6AN8 tube fail while the chassis was on the bench. 5th IF. The Pentode section just quit conducting. Filament is OK. I, of course, initially thought some component went bad. Luckily it was just the tube.

I found that most of the dag came off of the CRT so I had to replace it.

I also uploaded a photo of a service tag from 1956, half a century ago!

In the short time I have played with the set tonight after I got it assembled, I cannot get the Red purity to come in as it should. The manual states that the purity coil should be 1/4" from the tube base but I have to have it up against the yoke to have any kind of decent red field and it is still not that good. Any advancement of the the purity control away from full CCW just makes it worse. Not sure yet if I have just not found the sweet spot or if I have a problem. I'd be interested in any experiences in this area.

It is great to see this old girl running.

[ChuckA]

Tim,

I have some NOS 50 ohm CT pots, if you want one let me know.

Chuck

[Sandy G]

Wow ! An' ANOTHER one rises from the dead...Great !

[Pete Deksnis]

Originally Posted by Tim

The manual states that the purity coil should be 1/4" from the tube base but I have to have it up against the yoke to have any kind of decent red field and it is still not that good.

Congratulations Tim. My own static convergence/purity assembly clamp sweet spot is 3/4-in. from the tube base, which puts it pretty close to the yoke. Also a reminder. Make adjustments by rotating the black disk while holding (if necessary) the mu metal shield assembly clamped to the tube neck in its proper position (blue static convergence magnet up).

[Tim]

Thanks for the offer Chuck. I'll keep that in mind. Thanks also to Terry for sending me those peaking coils.

I appreciate the advice Pete. I realized that after a while but it still did not seem to be working as it should. Question on the orientation - is the access hole for the clamp on the left? That is where the manual says it should be and where mine is but I saw a photo of a set with it on the right.

I'll get back on it tomorrow or Saturday. We had the family over tonight for Thanksgiving and I learned long ago that alcohol and High Voltage do not mix well.

[Pete Deksnis]

Mine is on the left also. The braided lead seems to be long enough to be dressed over to the right as well. Doesn't matter. Just so one of the static convergence magnets is straight up (that'll make it the 'blue' magnet).

For purity adjustments, I pull the field neutralizing coil plug (three prong) rather than center the pot. And as a reminder be sure you have the yoke back as far as possible.

[Tim]

Hi folks and thanks for the coils Terry.

The repaired field neutralizing pot seems to be holding OK.

I have had some time to work on it and I resolved the purity problem. I discovered that when I installed the fuse I had put the coil wire on one side of the fuse and the pot on the other. The potential difference across the 3 ohm fuse meant that there was always current flowing through the purity coil, even when the pot was full ccw. Moving the wire allowed the purity to be adjusted. I have to remove the CRT again so I did not dial it in 100% but it is very good.

Then I went on to convergence and I found that, after much twiddling, I cannot get the top and bottom as close as I would like. Blue will not converge with the green and red. I have attached a shot of what it looks like. I also have to have the focus control full CW and feel like i'd like it to go a very slight bit more. Focus voltage is 3kv at this setting. I'd be interested in others experiences in this area.

The only other major issue is that depending on content, the HV swings from about 16KV to 20KV. The focus voltage sometimes drops to zero when the HV is minimum and the screen becomes a massive blur. It then recovers when the screen content becomes darker. The focus and HV regulator tubes are NOS and the HV shunt regulator tests good but I do not have another to sub it. Could this be possibly caused by driving it direct from cable and the front end is being overloaded? The test generator also causes this same problem. I have not yet tried another source. Any comments on this phenomena would be appreciated.

The set is very watchable from a distance and I am pleased with the progress so far. I have attached some screen shots. My camera is not accurately displaying the color of the bars though. The Yellow looks more yellow on the screen and the blue is darker than the camera shows. I also cannot see the moire' on the screen that the camera is picking up.

[John Folsom]

Tim,

Congratulations!

Convergence is a tricky business, as I am sure Pete can tell you. You may know this, but you will find the static and dynamic convergence portions of the procedure tent to be iterative. Once you have done static then dynamic convergence, go back and re-tweak static and then dynamic convergence. You may iterate to a better solution. I assume you have degaussed the set? If not, this may also help with purity and convergence.

The HV performance on the CT100 is always a bit disappointing. When it "blooms" and gets a dark screen with a fuzzy blob, it is an indication your HV supply is overloaded. Reduce the brightness and contrast to a lower level. The tendency is to turn up the brightness and contrast for a good picture, and then when a scene comes with lots of white content, the HV supply cannot meet the demand and the HV and focus drop out of regulation. I do not suspect there is anything wrong with the set, just the irresistible temptation to turn it up a bit too much.

[Bobby Brady]

I wonder if this one has a new CRT or a good old one. I guess we still can't rebuild the 15G?

I wonder about those other '54 models that have been discussed here like at least one Motorola and one Zenith. It would be great to see those three sets all working for picture quality. I am guessing they were all pretty equal.

Does anybody have any stories from people who actually had one in '54?

[Steve D.]

Tim,

Kudos on an outstanding job of troubleshooting and bringing your CT-100 back on line. I agree with John Folsom, that after all is done with convergence, purity set up and degaussing, 100% perfect convergence may still elude you. The moire effect is common with digital screen shots.

-Steve D.

[Tim]

Thanks for the comments guys.

John:

Yes, convergence can be tricky. I just was going around in circles on this with the few handles there are and not making it any better. It was concerning me that I was at the end of the adjustments, including focus, and have no more range. Is it typical for the focus to be up against the clockwise stop?

This HV issue I guess is normal but it is hard to believe it was that way when it was designed, that the owners could not turn up the brightness and contrast without a complete focus meltdown. My brightnes and contrast were set about 75%. Is this a component age thing or is it the belief that this was always that way?

Bobby:
The CRT is probably the original but it still has good emission. The date code of the CRT is the 26th week of 1954. Most of the other tubes in the set are dated the 12th week of 54.

Thanks Steve. It is always good to learn what is considered technically "normal" for a model set. If this is as good as it gets then so be it. Interesting that you mention degaussing as I was considering that but did not do it as this thing was sitting idle for so many years. I have to remove the CRT again before I set it up for good so I'll leave it as it is and try to walk it in better when I get it moved upstairs and degauss it. I guess degaussing would be regular maintenance for this set. Has anyone had any problems using a standard degaussing coil and procedure on a 15GP22?

[Pete Deksnis]

Great work, Tim. Missed the fun earlier in the day cause I'm in Michigan for a grandson's first birthday.

As John indicated, convergence is something of a skill to be developed. Keep at it. As I see it, what you have will produce a good picture, but there is also room for improvement if you want to spend the time. As for the blooming. Join the club. I suspect that RCA/NBC showed off the Model 5's on Jan. 1, 1954 in a dark room to avoid the blooming thing and probably to eliminate reflections from all that glass. I've used a regular '70's-era degaussing coil on the 15GP22 but couldn't notice any particular improvement. I've noticed the resolution of the picture improve as convergence improved, as you would expect. But it really looks impressive, particularly when the source is a live sporting event shot with hi-def cameras, perhaps because, as old-tv-nut has indicated, the hi-def system standards specify camera matrix characteristics.

It's back to NJ for me tomorrow.

Pete

[Pete Deksnis]

... re the focus control: no, it shouldn't be at the end of the pot of course. Could be the 50-meg resistor in series with the pot or, let's hope not, the vertical convergence transformer could be heading south. That 0.01-uF filter cap on the focus line has no doubt been replaced and therefor is not much of a suspect. To start with, I'd make sure the series string is okay.

[fujifrontier]

*cries*

[Tim]

Glad you had a great time with your family Pete. Have a good trip back East. Thanks for the encouragement and the club initiation.

I appreciate the sentiment Fujifrontier. Hang in there, there is a whole lot of fun in the quest.