View Full Version : Brought a 21CT55 back from the ETF!

Electronic M
05-31-2017, 01:22 PM
I've been wanting a major league early color set since my teen years reading about the CT-100 and the early days of color, and I finally scored one. The one from this thread.

There is quite a lot behind the scenes that goes into the purchase of a set that cost the better part of one my cars...I'd like to thank Larry W.(El Predicta) for selling it to me, Crist Rigott for transporting it well on the long trip from Texas to Ohio, and our founder Tim P. (Kamakiri) for passing on it, which allowed me the chance to buy it, as well as for the sound guidance given.

It survived both trips well. I requested that it be transported face down with the chassis and pencil box removed (and it rode that way on both legs of it's journey). The cabinet, chassis, CRT, and small parts box all survived the journey unscathed.

It now rests in my basement waiting it's eventual turn on the work bench. I'm planning to go slowly and methodically on this set once I start. I want to take the time to read up on these, and have all the right parts and prep. Aside from an orange drop the under chassis looks virginal, and I'm very tempted to do a restuff of the capacitors on this set. ( ( ( ( ( ( ( ( (

As you can see the chassis and cabinet serial numbers match, but the lid and cabinet 4 digit numbers do not, which I assume means at some point someone 'borrowed' a new top panel for it off of a different set.

I hope to get better pictures of it taken/posted soon.

And in closing: Whoopie, I finally have one of the 'holy grail' color sets! :banana::banana::banana::D

06-01-2017, 12:54 AM
Awesome! I'm looking forward to reading about your progress.

06-01-2017, 12:13 PM
Very cool, Tom. Congratulations!

I'm looking forward to following the restoration.


Phil Nelson
06-01-2017, 12:47 PM
I'm planning to go slowly and methodically on this set once I start. I want to take the time to read up on these, and have all the right parts and prep.That's a good approach. Take your time and enjoy the process. There are not a lot of these out there, so make the most of this opportunity.

Phil Nelson
Phil's Old Radios

Steve D.
06-02-2017, 01:05 PM
Quote: "As you can see the chassis and cabinet serial numbers match, but the lid and cabinet 4 digit numbers do not, which I assume means at some point someone 'borrowed' a new top panel for it off of a different set."


Different cabinet tops and cabinet #'s were common. As on the assembly line the tops & cabinets weren't always in sync. Also, sets that didn't pass the final inspection were pulled from the line and repaired. This also separated tops from cabinets and what ever top was handy was used prior to final packing and shipping. This also occurred on the CT-100 line durning its assembly.

-Steve D.

06-02-2017, 03:39 PM
Congratulations on acquiring this rare television. Pull out the wood piece that covers the front user controls. There should be a serial number stamped on the back.

06-02-2017, 04:33 PM
A little late to the party (been out of town) but congratulations!

06-11-2017, 08:38 PM
Congratulations!!!! A major achievement in early Color TV, and a great set to own. And in great hands as a VK Moderator. Enjoy and be proud!

Electronic M
01-17-2018, 10:36 AM
So....A lot of stuff has happened since I last posted... :D ( ( (

Back on new years eve, I decided: "dagnabbit I'm at least going to start the resto this year!".
I took shots of the chassis organized my parts and got ready to rebuild some caps.
Before pictures: ( ( ( (

I knew I'd have to find paper shells to stuff to sub for the bumblebees and white ceramic tubulars, but what eventually really frazzled me was the realization all the 'paper caps' were Dumont Duramold Bakelitized tubulars....Essentially bumblebees with a paper jacket molded on. I had some samples from other sets that I attacked with various methods (heat and dremmel), and after a few tries, I concluded there is no practical means of separating the guts and the paper sleeve without ruining the sleave. After nearly giving up on restuffing (part of me wishes I had since restuffing that many caps is a LOT of work) I came to the conclusion "heck if I was going to find alternate caps to restuff for ~6-10 of them, why not just do it for all of them?", and off I went. (hoarder alert! :D)I've got a bankers box worth of can lytics, paper caps, vintage molded plugs, and other interesting defective parts I've saved since the beginning of my resto work. From that box, I was able to pull re-stuffable paper caps to restuff in place of the originals. Since I found Sprague and Aerovox in the set I tried to stick as much as I could to those as the new shells. I gutted MANY paper shells, saving the wax and altering a few label numbers as needed, selected shells slightly smaller than original where possible to open up chassis space, and placed modern caps of the correct value in the shells filling some of the extra internal space with paper towel scraps (to conserve wax) than sealing the ends with the saved wax.
There were 3 orange drops from vintage repair work that I decided to leave alone. And in the HV cage I basically decided to not restuff anything (I figure smaller caps are harder to arc to)...Except the .22uF cap since I had one restuffed cap laying around.
Every restuffed cap has a red band on it, to denote the restuff.
The original paper caps are labeled with the Sam's ID number in the 'bad parts' bag.
I decided to mimic Christ Riggot's cap rebuilding technique on the multi-section lytics making a central wire bundle for the cap pack and substituting a piece oa aluminum from spare cans for his PVC section. The 4 cans under the seleniums I did my way: drill one hole per lead of the replacement cap through the wafer near the terminals and wire them up....Also since 2 had cardboard tubes I simply pulled the cardboard off, beheaded the can, put the new cap in and placed the cardboard tube over the topless can...I then decided to copy that on the metal cans by stealing the cardboard off other spare caps I had...It is easier and you barely see those caps anyway.
The result: ( ( (

I need to order more parts...All the tubular lytics 50V and under on the underside of the main chassis are still untouched, the 4uF 350V cap on the RED video amp board consists of 2 10uF 150V parts in series tacked in since I mistakenly ordered 2 3.9uF 450V caps instead of the 3 I needed, and the ballast resistor is dead (I kludged together a sub with series-parallel parts but it is not worthy of the final work).

All the white peaking coils were predictably wide open and got replaced...With 2 exceptions: The one under the IF shield was fine, and one of the demod-matrix coupling coils was a brown replacement probably from the 60's (shows how lousy those coils were that techs were changing them back then).

Powering it up on saturday got me a raster, sound and 10KV of HV...After some head scratching I finally pulled the 6BK4 completely out (it's top is so close the HV rect cathode that disconnecting the 6BK4 top cap had no effect!). The grid of the 6BK4 was too positive, and tacking in some parallel resistance with the 4.7M got grid voltage back in a range where the HV pot works decently. With the reg out it can do about 28KV. With the reg in I had it set at 25KV. Based on the grid voltage that was producing that regulation VS the listed voltage on the schematic I probably need to replace the HV reg tube and do more work on the circuit. The 6BK4 is one of the oldest I've seen. It sort of looks like they soldered the plate together and then it redplated or something. ( ( (

01-17-2018, 11:01 AM
Beautiful! Keep at it!

01-17-2018, 11:38 AM
Looking great, Tom, congratulations! So much more going on there, as compared to my CTC-7, which is the oldest color set I own, and the oldest color set I have ever worked on! Good to see results, even on the test crt, this should be a really nice performer, before long!

01-17-2018, 01:44 PM
All the white peaking coils were predictably wide open and got replaced...With 2 exceptions: The one under the IF shield was fine, and one of the demod-matrix coupling coils was a brown replacement probably from the 60's (shows how lousy those coils were that techs were changing them back then).

Tom, what parts did you replace the old peaking coils with?


Electronic M
01-17-2018, 02:11 PM
Thanks guys!

Splitting text past the 16 pic limit above.

I wanted to do the horizontal setup. but I could not really get video through the set with my ch13 basement modulator...I was able to get what looked like weak fuzzy sync bars and it looked like the horizontal was off freq. And I could get video waveforms on the bench, but no video with the chassis in the cabinet. I began to realize I was chasing my tail: I could not scope the Horizontal section and completely adjust it (can't adjust it is your not sure it is on frequency) in the cabinet or drive the set with my other bench equipment, but with the deflection disabled on the bench the AGC was probably being affected and there was no CRT to confirm injected or received video was being handled appropriately.

I then grabbed a test jig given to me by Dieseljeep and began trying to figure out how to connect it...There was no listing for the CTC-2B in 2 of the manuals I skimmed, and the adapters I have are mostly solid state era with some tube rectangular mixed in....Combing through I found an adapter that I recognized is for the yoke of a Zenith 15Y6C15 (a set in my collection) I was able with the Zenith schematic to decipher the adapter wiring color code and make a new yoke adapter for the CTC-2B (I can post up the pinout if anyone is curious). From there the HV and CRT connections were straightforward, and dynamic convergence I outright skipped connecting.

H out cathode current was down a lot VS its value with the correct yoke, and if the HV was connected to the jig there were some concerning noises, but for 30 sec raster duration powerups, this was sufficient. I began testing tubes and injecting video with the B&K analyst...I quickly found that the lumina chain was dead before the 2nd video amp. Then I found the contrast pot was open and the carbon track at the ends was gone. I also solved the mystery of there being 2 contrast pots on the shaft, but the front pot only using 1 lug. comparing the Sam's I was working off of to the RCA service clinic I found my set's contrast circuit is an in-between design. The rear pot on the shaft (delay line output) is wired according to the RCA manual, but the front pot (secondary chroma gain) is omitted, but used as a terminal strip/tie point like in the Sam's. I found a usable pot, but unfortunately, I had to remove both pots since the Allen key set screws on the shaft coupler between pots is frozen. I've got a new pot cobbled in, but will probably need to revisit this. Here are pics of the original and my sloppy repair. ( (

I did some more playing around with the B&K analyst injecting video and RF, and at one point noticed there were nice color bars from the analyst....I was SO focused on troubleshooting the IF's refusal to pass decent lumina that I turned off the distracting color on the analyst without thinking about what I was seeing:stupid:....About 30 minutes later during a restroom break, it finally hit me: "holey crap the color circuits are working, aren't they!?".:eek:....
The color circuits seem to be working and in or somewhat close to proper adjustment.:thmbsp: (

After checking that, I remembered something useful: Phil has an article about building a video amp for composite video injection for the CTC-2 on his site...I whipped one up last night and now have a good way to feed it video. I built it with a twist. I added a switch to go between IF and external video so if I can fix the RF/IF issue I can pick my input method. ( ( ( (

With that I can finally tune the horizontal stage up and KNOW that it is in sync...Which is the plan going forward.
I also intend to check the tuner on a different channel for good measure.

I took over 100 pictures of it and don't feel like posting them 16 (VK's pictures per post limit) at a time so here is a link to the rest: Lots of chassis pictures, and some more screenshots there.

A missed points from the cap rebuild discussion: on the tubular lytics I tried a new technique. I normally slice an end completely off, but found only slicing most of the way through leaves a nice hinge that keeps more structure in the rebuilt cap. (

Someone had added piggyback fuse replacements. That seems normal till you notice they used higher amp fuses and the larger B+ fuse had a MacGuyver style replacement...When the Piggyback spare blew, they simply stuck some aluminum foil in parallel! :yikes::no: Only way they could have made it derpier is if they had used a foil gum wrapper instead of straight foil. ( (

Electronic M
01-17-2018, 02:14 PM
Tom, what parts did you replace the old peaking coils with?

See link.
Digikey still stocks them.

01-17-2018, 06:55 PM
See link.
Digikey still stocks them.
Thank you, and thanks also for expanding my vocabulary. I never heard of derp, derpy, derpier before. Not sure if I'll ever remember to use them.


01-18-2018, 12:37 AM
Looks like you are comitted to putting in a huge effort on this set as you are intending to re-stuff the paper caps etc. It would be a shame after all the work you are going to put into this set if your flyback took a dump.

With that in mind you can take this advice and do what you will with it. During the restoration of my CT55, my flyback took a crap. I was able to obtain a replacement due to the generosity of John Folsom who was probably the only person in the world with a NOS replacement flyback for this set. Later on after I got the new flyback up and the set was running, the HV went down again. This time it was the 30KV doorknob. I obtained a new 40KV 2000pf replacement and with some small hardware mods it replaced the original quite nicely.

Upon reflecting as to the cause of the failure of the original flyback, I came to the conclusion that the original doorknob was probably leaking and placing an extra load on the flyback. Combined with the poor ventilation of this HV cage desing, it was more than the flyback could endure. More recently, I was involved with the replacing of another one of these failure prone doorknobs in the 15" GE color set that came from Colin Wood.

I see from your photos on Flicker, that your flyback appears to have been overheated. I can see from the photos it has sagging wax and drippings.

If I were in your shoes, I would buy some insurance.

Get a new 40KV 2000PF doorknob and replace the OEM POS that is in your set presently, to insure that you have a doorknob that is not leaking.

IN addition, the HV cage on this set is very poorly ventilated. Get a small muffin fan, cut a hole in the side of the HV box and force cool that flyback.

Your flyback has already been punished enough from sitting inside what is basically an oven. Don't take a chance on killing your flyback. Almost anything else in this set can be replaced, if the flyback takes a dump you will kick yourself around the block if you did not take some prophylactic measures to safeguard it. And it could fail even if you do.

My flyback runs cool as a cucumber with the new doorknob and force cooling the HV cage with the muffin fan. Go for a fan that has a very quiet sound rating instead of a high CFM. With the volume set at a normal listening level you will not be able to hear the fan running.

Good Luck

01-19-2018, 01:15 PM
Very good advise from Bob. It astounds me how any of the components can survive literally mm’s from heat producing tubes. A recipe for failure. We also added a fan in our 21CT55 by cutting off the “chimney”. The hole is already cut in that location. Added a switch to shut it off if needed. As an added precaution, the power is regulated with a Furman power conditioner.

We had a failure after several months of operation. Suddenly lost convergence, focus and the picture shrunk. “Oh no, the flyback!” We traced the problem to an open resistor buried under the damper tube.

The High Voltage was reduced to 10 KV with this failure. It now adjusts nicely from 18 KV to 21 KV as it should. The resistor was an original (made by International Rectifier) special film type, 3.4 Megohm 3 watt. It was replaced with QTY 2 (in series) OHMITE 2.2 Megohm 2 Watt film type which now makes the new resistor a 4 watt unit which is a 25% upgrade for power dissipation.

Did you check the serial number stamped on the wood pull out under the pencil box? Wishing you continued success in the restoration.

A few photos of the bad boy resistor, replacement and fan:

Electronic M
01-20-2018, 11:24 AM
Before the HV reg (more specifically that 4.5M resistor feeding its grid that Etype mistakenly refers to as a 3.4M above) was identified the large doorknob cap was briefly my prime suspect in the low HV issue. If that doorknob is a high failure part as you imply then I will look into replacing it. Since the first powerup, I have been running the set with all removable panels of the HV cage removed for maximum ventilation and ease of access...I suspect that may be contributing to the reception issues. I will be considering means of improving air circulation. If possible I'd like to refrain from putting holes in the original metal so I may make modified replica sides for the HV cage as mounting points for the fan(s).

Since I had some good free time until the end of this week the goal was to do as much as I can. I started a new job late this week...Between a swap meet this weekend and work it may be a while before I can sink more time into this, however, I'm pleased I was able to get this far in the time I've spent.

01-20-2018, 05:33 PM
Off to a great start with your complete restore to original restoration. I'm impressed with your progress so far, even to re stuffing failed capacitors!
From my experience with this beast, I would advise mounting a single pole toggle switch in series with the +400v deflection system fuze.The rear chassis near the HV adjust pot is were mine is. This "kill switch" would enable instant HV system shutdown and restart without taking the entire 21CT55 down and have to wait for a complete TV start up. During work on the deflection system, I never leave the room without killing the + 400v power! I might be a slow learner, but not that slow.

Electronic M
01-28-2018, 12:51 AM
So first the bad news: my Blu-ray player has the zoom settings in a retarded state that pillar-boxes 4:3 content to have bars on the sides, and I don't have a remote to fix that menu setting....

The good news in video form...Click to visit then click to watch: :banana: ( ( (
Of all the Model5/CT-100/21CT55 screenshots and videos I've seen on the internet, I can't ever recall even one showing the RCA CED/Selectavision intro theme being fed to one of these sets....How this has not occurred to anyone before I can't fathom....But I can put two of RCA's coolest engineering achievements together, and let people nerd out to it. :D

And now some obligatory Wizard of OZ screenshots: ( ( ( ( ( ( (

'How did it get to this point?' you ask....Well After rearranging some stuff I decided to move the cabinet to the workbench gather/make extenders for the yoke, CRT and speaker (but not the dynamic convergence...That reaches if the chassis is not mounted), and then go about dipping the H out cathode current with the osc in sync and it's waveform correct. I dipped the current using the linearity and drive controls. It is at a steady 217mA with the B+ at 390V....I've found the B+ affects it too. I decided to dip the B+ to 375V where the cathode current is around 205mA....Running it that way for an hour the fly is just slightly above my body temp which I think is quite a healthy temp for it. (

I then adjusted the vert section and centering and fed it color bars....I was VERY disappointed and confused. The color bars made NO sense at all and adjusting the tint did not help. I also had to super glue the red static convergence knob back on to the magnet. It broke off with a gentle twist.... I went on to check the tuner on channel 7 and 13. Seven got nothing and 13 did not improve, but I discovered 12 will pass sound from 13 and the monochrome video....It will also pass the local NPR station(I can see the tower and tune it on otherwise dead FM tuners) on part of the fine tuning range on channel 12. What is up with that?
That all (except for the hour run) was Wednesday and I gave up for the night.

Earlier today I decided to get back on it. I decided to do the purity adjustment. I did try to prep for it Wednesday, but the screen controls did not kill any gun or work as expected in terms of color change. I found it easiest to short the B and G grids to ground to leave only Red...It did not look red at all, but what the hell. First try I got much more red on the screen, a few back and forths with static convergence, purity rings and eventually the face magnets, and I got it fairly good (worst primary pictured)....Best yet I turned up the color adjusted the tint and got good SANE color bars. It seems the purity was SO far off before that the guns were all completely scanning each others phosphor! ( (

I then pulled the vert tube, shorted the CRT grids together and grounded them through a 100K resistor. I set R and G to produce a reddish yellow (ISTR hearing these sets were meant to have a slightly reddish grey scale) then blue for white. I then removed the jumpers. plugged the vert tube back in and adjusted the B and G drives for slightly reddish whites. I need to figure out the B and G balance controls (I adjusted the outer one by accident).

So far it is REALLY good. If the RF/IF system would only pass color I'd be about content with performance.

I need to order new resistors for the focus/HV reg system...I also need a need a new HV probe...My favorite/accurate one fell off this set 4' onto a concrete floor and shattered. That probe probably saw 8-10 years of service since I got it (plays taps softly).

BTW / PS I added pics of my video amp and the contrast control/it's kludge replacement to an earlier post on the first page of the thread.

01-28-2018, 01:44 AM
Tom, you've made great progress on your CTC2b set. :thmbsp:

Electronic M
01-29-2018, 10:20 PM
Thanks Ed.

I did some more fooling around and found the IF will pass color, but the fine tuning setting for that makes the luminance and sound noisy. For now, at the very least it is an awesome monitor...with a tuner that has issues. ( ( by Tom Carlson (, on Flickr

I want to improve a few small things, then I'll have to decide whether to deal with the cabinet or alignment first.

01-31-2018, 09:12 AM
The High Voltage was reduced to 10 KV with this failure. It now adjusts nicely from 18 KV to 21 KV as it should.

Once again, the HV specification for the 21-CT-55 is NOT 21kv. It is 25, please stop spreading misinformation. If you want to run your own set that way, that is your business. Donít misquote service literature to others.