I'm beginning to think color sets are more trouble than they're worth.
 

While watching my Zenith roundie which gets very light usage, the vertical collapsed for a second then came back. It often jitters at the top an bottom as though the raster is about to collapse the vertical. This is about the fourth time I have had vertical problems with this set caused by varoius things. My tube type black and white sets while not immune to breakdowns are far more reliable with even more use. Also I noticed that the convergence needs touching up and the greyscale needs to be tweaked as well. I'm thinking it is just a little bit too maintenance intensive.

Did you clean out/replace the vertical height pot? They are prone to tin whiskers and being noisy due to age, but it could also be the vert position pot. Should be an easy fix.

Funny you should mention that. This week I was working on a 1930s Stewart Warner radio that had a serious case of dendrites inside a potentiometer:

http://antiqueradio.org/art/StewartW...rDendrites.jpg

"Dendrites" are the fuzzy, bristly stuff growing down from above, in that view. (At least in NASA terminology. They use the term "whisker" for a slightly different phenomenon, the growth of a long, single metal hair rather than a bunch of fuzz.)

First time around, I opened up the pot case and gave it the usual DeOxit treatment without looking very closely. When problems persisted, I reopened it and discovered all that cute metal fuzz making intermittent shorts inside.

Dendrites clean off easily, but you can't count on simple spraying to get rid of them. They (or whiskers) can also form on the outside of a control, making a short from the control case or terminals to chassis or some other components.

Yet another reason to clean, clean, clean these old chassis, especially if they have been in a moist environment.

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

BINGO!!! That was the problem with my Admiral 26R12. The height collapsed and the control did not "control" the voltage. A good cleaning of the pot fixed it. It was my first experience with tin whiskers...

Please, Don't give up...

I believe most if not all Zenith roundies had a dual section 3 lead disc capacitor in the vertical circuit. When it would start to go, you could have all kinds of goofy vertical problems. If it were flat out bad the vertical would pull up from the bottom. As I recall, hitting it with circuit freeze sometimes worked when there were weird symptoms.
If the set came in with a vert problem that was the first thing suspected, and many times the problem. I replaced a lot them as preventive maintenance.
Good luck.
Phil

Imagine all of the problems and headaches that the new flat screen TVs are all going to have. All electronics are now required by government regulations to use pure tin parts. Tin whisker city!

The tin whiskering problem is why high reliability equipment like military and space hardware was specifically exempted from the lead-free solder requirements of the RoHS agreements.

Lots of scary pictures and technical data on tin whisker issues here:

http://nepp.nasa.gov/WHISKER/

Note: 'supposed' to be exempt. I had a circuit card from a piece of MH-53 gear give me issues that I eventually traced to a tin whisker on a power diode. It was shorting to ground. Apparently the contractors didn't get the memo. lol No usually a huge deal because most stuff is conformal coated anyhow, but not all.

restoring these old sets really isn't much differenct than restoring old cars. Tube sets by their nature generated much more heat which helped increase failure rate. Couple that with the fact that any existing sets today have components that have far exceeded their original shelf life. That's why I don't throw anything away because the chances of finding replacements are getting few and far between

Well.... I love em, but they CAN be a pain in the ass. I remember as a kid working in my Uncles shop (and getting to go on housecalls!) that it wasn't uncommon to have to service some sets 3 times a year. This was in the early 80's and even then we pushed to get some customers to "move up" to a solid state set. In 1980 a CTC-16 would have been 15-16 years old, and the worst RCA chassis (CTC-38) would have been about 12. My memory of all the sets that got pitched has caused me to grab em now when I find one at an estate sale. Now.. 30+ years later, I'm sure age hasn't been kind to the components of the tube sets we love. I couldn't imagine using one as an exclusive daily driver now...........

Both of my Zeniths, a M and an N chassis have eaten their vertical output transformers. The M ate a second Zenith vertical output. I replaced all with Thordarson and so far they are fine. They started off with a slightly jumpy vertical then went to what looked like severe interference and overheating resistors in the vertcal output stage. The convergence winding was leaking to the primary winding.
Tin whiskers have mainly showed up in my old Admiral black and whites.

My Zenith 25MC33 chassis has been through two vertical output transformers too. Mine had thenexact same symptoms and failure mode.

I like to think the sets we all still have are the survivors among all the lemons.

Reality is that every manufacturer used a few lousy parts somewhere and sets got junked for something as simple as a single generic part or as justified as a bad kinescope. The sets we have are here because of our preservation interest more than performance or economy.

I junked alot of sets 30+ years ago due to bad flybacks or CRTs rather than hold them and wait for a found part that didn't cost as much as the Jobber quoted.
A nice big warehouse would have been the ticket for saving the all the collective good parts.

I don't begrudge the sets for their appetites. We've gotten used to the BPC's running 10+ years without problem and then their flybacks crash and they go to the trash. I use my tube colors about 5 hours a week, mostly to watch something good (not the usual nite time TV). The hungriest piece I have is a McIntosh MI-3 scope. If there is a 6EA8 tube within ten feet of it, it's like a cat on a mouse! It goes thru them quite regularly! Most docile is my RCA KCS 166 black and white portable. It just works.
Now to see how hungry my RCA "Latham" is going to be

I had a CTC38 that I used as a daily driver for quite a number of years in the late 70's and 80's. One of the best and most reliable TVs I ever owned, for what it's worth...

Boy you were lucky on that one hi volt. I shouldn't complain too much about them as they were our "bread and butter" in the repair field. But man.. they loved to eat flybacks and 6GH8's. That and the CTC-39 were RCA's last console TV tube chassis and RCA really went "on the cheap" when they cranked those out. However.. you could usually repair em in-house because for the most part it WAS a 6GH8, and if it was a flyback.. one of the easiest tube chassis to remove.

RCA introduced the 2-board "cheap chassis" as a space saving to make the first 19" sets, the CTC19, then as a budget set, the last roundie CTC20, then the CTC 24, 31, 38 and 39. There were dogs and some lived longer, trouble-free lives.

A theory why some RCA's ate flybacks: All the substitution books said a plain ol' 3A3 could be replaced by a 3A3C, but it was shorter by 1/8", preventing the plate cap from fully seating into the fly. The resulting arcing was sometimes evidenced by poor horizontal lock.

The 19's were definitely junk but put a lot of bread on the table.

I never thought the CTC38,39's were that bad. The only HV rectifiers I had in my caddie were 3DB3's. Just about every RCA was hard on flybacks. The 19's 24's, 31's and the 20's were not as good as the 38 family. I have a CTC51K that isn't that great either. :nono:

Would you happen to know the Thordarson number for the vertical output transformer for the 24NC31Z chassis? I had mine rebuilt, but it still acts up.

I have the 25MC33 chassis and the Thordarson part number is 26S61 which is a direct replacement for Zenith part number 95-2139. I don't know if your chassis uses the same part but I offer the information just in case.

Yeah, they ARE...That's why is sO GREAT when somebody restores one to its original glory & sets it up right...

Thordarson transformer
 

My 25nc38 has (had) a 95-2345 vertical output transformer. The thordarson is a 26S44. I've been using it a while now and it works fine!

Speaking of diehard Zeniths....My Aunt/Uncle had a Zenith 25MC33 (36??) it was ALWAYS on. It stayed on through lightning storms and everything else - I remember saying to my mom, see we don't need to turn the TV off during a storm!

They traded it on a slider-tuned-varactor Zenith in 1977 before I knew it. Saw my Aunt to show the her our new baby girl last Saturday and I asked about that set. I confirmed what I remember from many years back. (No wonder I never saw one at the curb, I only fixed a few Zenith Roundies, and get one for my collection in a heart beat!)

It was bought with wedding money in 1965, The store that sold it also sold most Zeniths to our family and, on rare occasions, serviced it as they did my parents and grandma's TV's, both 1971 Zeniths. The Owner made the house calls but had a good bench tech at the shop. I wanted to work for him, too. My Aunt said they only had it worked on a few times and not because it quit, no, it was tuner cleaning, weak tubes and control touch-ups usually done at once.

He said the reason this old roundie lasted so long was that it was left ON ALL DAY as opposed to OURS and grandma that turned TV on only to watch something (kind of what us collectors do today) and off again several times IN a day. Off when the news was over, off for mealtimes, off when the sun came out......kinda hard on everything when you think about it.