My "new" 1954 CTC2B 21CT55 21" roundie

[walterbeers]

Well, here is the latest. I replaced the electrolytic caps in the power supply, however haven't yet replaced all of the electrolytic caps that are in the sets circuitry. I have the chassis on the bench, so hooked up the deflection yoke, convergence assembly, and of course the speaker, without the CRT connected, and of course with the horizontal output tube pulled. Applied power with my variac, (actually a switchable isolation transformer "pictured"). At about 50 volts AC I got about 200 volts (of the rated 400 volts) from the power supply, which I suspected. Then raised it to 75 volts AC, and got 300 volts out of the power supply, so gradually raised it to 100 volts AC, and got the rated 400 volts, so left it there for a bit. All tubes lit up, so I hooked up my converter box to the antenna terminals, and got audio. It became promising, so installed the 6BQ4 horizontal output tube. I began to get 20KV high voltage, but heard some arcing, smelled ozone and something getting hot. Then the 1/2 amp fuse in the horizontal output B+ popped, before I could disconnect the set. At least it wasn't the flyback, but I found a bad focus control, arcing internally running too hot to touch. Disconnected the lead providing the focus voltage to the pot, powered it up again, and WOOO!, almost 30 KV, and pop (just a loud arc) so pulled the power cord immediately. Looked at the schematic and I noticed that the regulator 6BD4/6BK4 derives it's bias off of the down side of the focus control, so that explains the excessive HV. Also before hand, I had replaced all of the peaking coils that were bad, (those tan round balls), which nearly all of them were open. (A common problem I have run into with several other sets). Oh yea, by the way, the selenium rectifiers have been replaced with silicon diodes. Also I intend to cover the small new power supply capacitors with cardboard insulator covers to make them look like the originals for appearance sake. Another thing I noticed was that the 6AN8 tube V11 (AGC and Sync Seperator started to glow bright blue, hopefully just a bad tube). So my next move is to find a suitable replacement for the 5 meg ohm focus control. Control is quite large but is only rated, according to the Sams at 1/2 watt, 5 meg ohm. RCA part number 79028. I know workman used to make some of these style controls and focus resistors, so hope I can find something that will work.

Oh yea, speaking of PI, well PIE, the kind you eat (from the post above), the best pies you can buy in the Omaha and Midwest area are frozen ones that are home made from the Village Pie Maker. They can be found in the HY-Vee stores, Bag and Save, and other locations. They are made in Nebraska, from a small company that several local women got together and decided to make a business of it. They use fresh fruit, (not frozen), and have Rhubarb, Cherry, Apple, Mix Berry, Peach and others. Look them up, just type in a search for the Village Pie Maker. Maybe they are even available in your area.

[Steve McVoy]

If you can't find a 5 meg pot of the original style, another option is to use a standard 2 meg one. The voltage differential across it will be small enough to prevent arcing. You will have to experiment with resistors on either side of it to total 5 megs and have good focus at the midpoint of the pot.

[walterbeers]

I am also going to have to find something to make and use for a yoke cover as the old one was crumbled beyond use. The yoke is slightly over 6 1/2 inches round and also I am wondering if a cover from another roundie yoke cover would fit. I know someone on here manufactured his own, and also heard of someone using a plastic paint can lid. Suggestions?

[dtvmcdonald]

Plastic top from some sort of food pail, for example, ice cream. May cost money,
but at least you can eat it.

For my CT-100 I just cut two pieces of cardboard into two overlapping
halfs, slipped them on the already assembled CRT neck, and taped them
together. You could do that with plastic sheet.

[miniman82]

coffee can top is what some have done.

[walterbeers]

I'll give the can lid/top a try. I might get some strange looks measuring can tops at the grocery store, but if I can find one 6 1/2 inches it might just work. Thing is though it has to be heavy enough to hold the copper ring along with the heavy (lead)? circular piece in place between the yoke and the convergence assembly. Are those pieces even really necessary? I have never seen them on any other roundie set, and also wonder what they are for. The heavy ring is held by the three stand offs with rubber pieces between. The stand offs go through the copper plate which was riveted on to the back side of the yoke cover. The heavy ring is not a magnet, as far as I can tell. It doesn't seem to be magnetic at all. Just a heavy ring. I wonder if I really need them. Oh, by the way there is a ground wire running to the copper ring.

[walterbeers]

Well, progress has been slow, but going in the right direction. I was able to find a 3 meg 3 watt pot for the focus control, and using a combination of 14 meg from one side of it to ground and 4.2 meg from the plate of the 3A2 V23 I was able to achieve around 4 KV, adjustable about a half a KV either way. That may be close enough, maybe not. Will have to experiment. Set powers up on the bench without the CRT attached, and have about 22KV at the second anode. The Sams, calls for 25 KV, but I don't remember any roundie running more than 22 to 24KV on the second anode. I will say that the dropping resistor I have in the power supply is only running the B+ at 375 volt, so I probably can get more high voltage if I go up to the full 400 volt rating. I have replaced all the electrolytic capacitors, leaving the cans intact, but most of the cans are disconnected and wired underneath. The power supply caps were taken out, and replaced on top, in which I intend to mount the cans over them making it look original. I'm now onto replacing all the paper wax capacitors, but I just ordered all of them today, so that is a major soldering task ahead for the next step. I was able to fashion a yoke cover from a Tupperware lid, and mounting the copper ring to it. I have no idea how things will turn out, and if the set will ever produce a good picture, if any? Once I get all the rest of the capacitors replaced I am going to power it up connected up to the CRT and see what happens. I have high hopes though. As I said, this is going be an on going 2 or more year project.

[pendulum]

Keep up the good work! Thanks for all the updates and the nice photos. I love the high voltage setups in these early color sets. They always look like a crazy science experiment.

[Titan1a]

Keeping in touch. Don't give up!

[Electronic M]

Don't forget the white video peaking coils under chassis....If those are open (which they tend to be) you will have video problems.

[jstout66]

Walter checked and changed all the peaking coils already. (I think only 2 were good)
We got to experience the joys of bad peaking coils on my 56 Motorola.

[Alastair E]

That heavy grey ring--Looks like its made of ferrite.

Could be to magnetically screen the scan-coils from the convergence-yoke--or vice-versa....

Not seen one like that on any UK Delta gun convergence-assembly....

[walterbeers]

I believe it is ferrite. A magnet will stick to it, but it's not magnetic itself and quite heavy. I also believe the it's to screen out the magnetic field between the yoke and the convergence coils. The copper ring, well, it has a ground wire running to it. I also wondered if it is was used to reduce X-radiation, however I think it would have to have lead in it then. I had never seen one of those ring setups on any roundie I had ever worked on till till I got this one. Does a CT100 model (the 15 inch set) use the same type of set up with the rings?

[walterbeers]

Here is the latest on the restoration of the 21CT55, CTC2B Oct 7, 2015 All wax caps have been changed out, except those mentioned below.

Well, I powered it up again on the bench, although it still needs a few more caps, 6 in total, 2 are already ordered from MCM. I have sound, vertical, high voltage, and video waveform (on my scope at all three CRT grid connections), and voltages are within range at the CRT socket proving that the set should produce some kind of picture or at least a raster, when I get it hooked up to the CRT. When I first powered it up, there was a buzz and a wisp of smoke somewhere in the audio section. After trying it again, and not being able to locate what got hot, sound came on just fine. I can get plenty of high voltage, although if I push any more than about 22kv, it sometimes arcs and snaps like a firecracker. Not sure where it is arcing. Flyback runs pretty warm, almost hot, after being on for 15 minutes or more in the center part of the flyback. Current being drawn by the horizontal output tube is normal, even a little on the lower side, 185ma, so that shouldn't be the cause of the warm flyback. I also still need a couple more tubes that check bad, a 12BH7, and a 6LN8. None of the tubes or capacitors that are still needed should affect the flyback. Power supply runs right at the rated 400 volts with 115 volt AC line. I want to get the other caps and tubes in there before I figure out how to hook it up to the CRT and still be able to service the chassis. I can either sit in on top, or on top of something right behind the set. I also still need to order a much longer piece of high voltage wire to hook up the set outside of the cabinet. Sams indicates that the high voltage should be at 25kv. I still wonder if that is higher than it needs to be. My biggest concern is that the flyback will be OK. If it goes up in smoke, well, finding one is almost impossible. I still have high hopes for the old 1954 set, as I have lots of time and $$ into it.

Today's update: Oct 08, 2015. Powered it up again, no snapping of HV at 24KV, so may just be moisture or dirt. Found the problem with the buzz and smoke up by the audio section. It was just a pinched wire, which runs upfront by the service adjustments. I don't think any damage was done. Flyback will get quite warm, even though the Horizontal output tube current is within the normal range. However the waveform at the grid of the horizontal output, (the sawtooth waveform) is flattening on the top. Picture attached. I noticed there are adjustments for wave shape, etc in the Sams, so I'm assuming that will take care of it. The waveform may be what is causing the flyback to get warm, mainly in the center of it close to the core of the transformer. The large ring for the high voltage winding remains cool. Yoke, convergence yoke, and magnets are ready to go back into the set. I have the possibility of getting a CRT test jig. An RCA. I'm not sure if I can use it with this set or not, but could also use it on my CTC9, and others. I am encouraged, I'm just taking it a little at a time.

[ohohyodafarted]

This chassis has a very large HV door knob cap mounted to the back side of the HV cage. On my set that door knob was bad, probably leaking. I purchased a 40KV replacement on ebay. I needed to modify some of the mounting hardware, but it works fine.

I would suggest that you check the big 30KV door knob to see if it is getting warm which would indicate leaking. If yours is leaking, I would replace it before it wipes out your flyback.

I also installed a small cooling fan in the side of my HV cage to keep my flyback temp nice and cool.

When I restored my CT55, I placed the cabinet next to my workbench and made extension cables to connect the chassis to the crt and other components in the cabinet.. That worked very well.

You may find this link to the page on my web site of some use.
http://antiquetvguy.com/WebPages/The...CA-21CT55.html