Restoring CT-100 #B1111566

[ChrisW6ATV]

With the 8TS30 all done, I have restarted on the CT-100. First, I made a complete list of all the resistors that were poorly replaced (combinations and similar; I much prefer to have everything match the original parts if possible). They are all at or near the proper values, so I may just leave them in until I get all of the bad caps replaced and see how well the chassis works.

[ChrisW6ATV]

This set is a rather massive project, I am finding out as I go along. Most of the wax capacitors were replaced, many as long ago as the 1960s based on likely date codes on the replacement caps, but those early replacements are "maroon beauties" (maroon-colored molded caps with the leads out the middle of each end, as opposed to "drop"-type radial dipped capacitors). Also, I am finding out that some of the replaced caps are lower-voltage ones than the values in the parts list, so I am going through every replaced part in this chassis to compare with what most likely should be there. This may be similar to what Phil did as he described earlier and on his Web site. In the process, I have decided I will restuff electrolytic cans if at all possible on every set I restore (including this one), because tracing back from randomly-installed replacements under the chassis is a pain in the neck that I do not want to burden future owners with.

Good news: I have the cabinet back, HV cage cover and controls I needed thanks to Dave A and another VK member. Following the rest of the capacitor research, I will next complete the analysis of the high-voltage section work needed, and then look into making an adapter to connect this chassis to my Sylvania CK3000 test jig.

What do you all think about those "maroon beauties"-are they likely good since they're from the 1960s or newer, or should I replace them now?

[miniman82]

If they aren't maroon drops I'd replace them, even those maroon drops can be suspect if used in sweep sections. The CTC-9 I had was full of them, but they didn't seem to cause any issues in that low hours set. It's still working well on all original parts with it's new owner, aside from the new 'lytics I replaced as a precaution.

I'm partial to orange drops myself, it's just what I've always used. But lately I've noticed that supplies of them can be hard to locate, particularly those oddball values like .0082 and the 1600v ones used across the vert output winding. I now just search Mouser or Allied for values, and just buy whatever brand comes up. Can't be picky these days it seems. Like Folsom says, "it's all about the spares".

[Phil Nelson]

Until I restored my CTC-7, I would have considered older "maroon drops" as good as new orange drops, but I couldn't get the sweep sections working right until they were all replaced. Based on that, I am now suspect of all older drop-type caps (I have seen some green and blue ones, too).

The failure mode may be something a little different than for paper caps. In these cases, I consider the TV the best "cap tester" in the world. It's possible that your set would work acceptably with the sort-of old maroon guys in place. I don't see any downside to seeing how it works with them in place, and later deciding whether to replace. On the other hand, you have it on the workbench now, and the maroon drops are not original components, so replacing the replacements is not destroying anything of great historical value.

It sounds like you're taking a methodical approach, which is great. I'm an impatient guy, always eager to see results on the screen. When working on my CT-100, I told myself it might be the last one I would ever lay hands on, so I tried to relax and enjoy the process.

Phil Nelson

[ChrisW6ATV]

Since I already plan to replace the substituted resistor combinations at a future time, I have decided to leave the maroon caps in until then as well, unless I find problems with them during initial testing of the chassis. That still leaves all of the electrolytics and a number of original paper caps to be replaced first. The set had working sound but arcing or other HV-cage problems as of when I got it, if I remember the descriptions. That area definitely needs work in any case. Thank you for your notes, Phil and Nick.

[miniman82]

Before you go any farther, I suggest you replace the focus HV cap coming off the wiper of the focus control. The one in my chassis was original and leaky, causing the demise of the focus control. It's a .01uf @ 6kv cap, Allied should have it in stock. One of those ASC tubulars.

[ChrisW6ATV]

Oh, thank you for that tip too. I had seen Steve McVoy mention that cap as well; I have it in my file of collected CT-100 repair tips and notes. My set's focus and convergence pots may have both already been replaced, but I am going to look closely at everything in the HV cage.

[miniman82]

A good once-over is never a bad idea. Does this set already have the replacement convergence transformer, or do you still need to drop John Folsom a line? If not you may as well get that out of the way, since his supply will not last forever.

[ChrisW6ATV]

That is the transformer in the box that sticks out from the back of the HV cage, right? Mine looks pretty new, but the box itself is odd; the underside looks like it has been patched with epoxy or another substance and then repainted. I will test the transformer.

[miniman82]

Yeah, it's a small steel box with the transformer potted in pitch. Honestly though if you see pitch on the inside, you might as well just replace it. You could test it with an ohm meter, but that will only tell you the resistance of the windings. Even if they ohm out in the ballpark, it could still fail upon application of HV. I'm of the mind that these particular transformers are just like old caps. There are only 2 types: those that have failed, and those that will. When it does you'll burn the focus pot, and I was not able to find a replacement for it which means making a non original mod. Deal breaker? Probably not, but avoidable? Completely.

The former owner of my CT-100 took the original one apart with the intention of rewinding it, here's the hole through the insulation that caused the primary to short to the secondary.

[ChrisW6ATV]

My set's transformer is not potted. It definitely looks relatively new (that is, 1970s or newer perhaps). It has two red wires coming out one side from the winding and blue, white, and brown wires coming out the other side. The lower of the two side pots (is that the focus?) has been replaced with a non-original-style control that I would describe as 1970s/80s or newer HV construction (a white plastic molded case with wires coming out the back). I will post a couple of pictures of that area of the HV cage when I get a chance. This set has had a lot of work done in the past, such as two new wires to the CRT connector, likely the convergence and focus (I may have already confirmed that a while back).

[miniman82]

Who knows, maybe someone had an original rewound years ago? John's new ones have a red/black pair for low voltage and a pair of white wires for the high voltage side.

[ChrisW6ATV]

Progress on this CT-100: I have replaced all of the remaining wax/paper capacitors and all of the electrolytics on the chassis, and "all" that should remain before first power-up is the work on the HV cage. Here are two pictures of it with a bit of clean-up I have done so far.






I have a list of work needed in there:
-Replace several parts that were previously replaced with incorrect values.
-Install a new filament winding for the 3A3 HV rectifier (it was removed when a solid-state replacement was put in).
-Modify the 6BD4 wiring (relocate items from tie-point pin 8 to a nearby unused terminal) so I can use a 6BK4 (which was already in the set when I got it anyway).
-Remove the remaining white silicone glopped around and repair any connections underneath.
-Clean everything in the cage as best as I can.

With all of this needed work, I am leaving the peaking coils and other parts alone until I see what happens after the HV cage work. This set is getting closer to being fired up!

[earlyfilm]

Originally Posted by ChrisW6ATV

Most of the wax capacitors were replaced, many as long ago as the 1960s based on likely date codes on the replacement caps, but those early replacements are "maroon beauties" (maroon-colored molded caps with the leads out the middle of each end, as opposed to "drop"-type radial dipped capacitors). . . . . . . . .

What do you all think about those "maroon beauties"-are they likely good since they're from the 1960s or newer, or should I replace them now?

Chris,

If the pictures of the "maroon beauties" shown in the bottom image in post 28 above are what you are talking about, then there are two answers.

If the replacement capacitors are genuine Sprague, they probably are OK but are nearing the end of their natural life.

However in about 1957-1959, there were a lot of counterfeit Spragues made that mostly failed within a few weeks. The best clue as to whether it is a genuine or counterfeit, is how level the yellow ink is. The counterfeits were marked with a rubber stamp by hand, while the genuine Spragues were machine labeled. Another clue is the fakes usually had a little more plastic extruded around the axel leads than the genuine.

During this time, the nationally known wholesale house where we bought our parts was fooled and sold these as a lower cost alternative. We were low on several popular values and bought a single order. After we had had three failures in 6 weeks, we brought these back to the wholesaler and demanded and got our money back, along with replacement genuine Sprague capacitors. We notified every customer who's set had used capacitors and had been repaired during this time frame and did a free inspection in home. On radios, the customer had to bring them back and we inspected those while they waited.

Apparently when Sprague made it too hot for the counterfeiter to sell these, they made the identical capacitors in several plastic colors with other fake labels. Most had either white or yellow ink, although I've seen a couple of ones with green and red ink. I've seen them labeled as Admiral, RCA, Motorola, Tung-sol, (yes, Tung-sol !!) and a other known and fake brands. They were often advertised in magazines and sold as major brand production over-runs, or manufacturer end-of-model-run surplus, even into the mid-1960's.

The radio bench made a 100% switch to the counterfeit parts, as we were out, while the TV bench just added them to their working stock. Many of the TV's that we pulled apart in the customer's home, on a large shop cloth, to check did not actually have one of the counterfeits in it.

Trust me, after this incident, the shop that I worked for started keeping a much more detailed component record attached to our file copy of the bill.

James

[Phil Nelson]

If things in your HV cage are covered with the usual black soot, isopropyl alcohol and a soft brush usually clean that up pretty well. Watch out for fine wires around the flyback.

Have fun!

Phil Nelson