RCA CTC-5 "Wescott" restoration

[bgadow]

After recapping mine, I couldn't get the HV to run. Horizontal frequency wouldn't go quite high enough. I finally figured out that I had put one end of a cap on the horizontal board through an extra hole...a hole that went to ground.

[DavGoodlin]

Im working on my Philco CTC11 clone, it has a tube crystal like that.

Last chassis to use them, both my CTC12s have a can.

[bandersen]

Progress update. Horizontal and vertical board done. Moving on to the sound.




Also took a closer look inside the HV box. Amazingly all the tubes appear to be original.
That includes the early 6BK4 shunt regular design with no integral x-ray shielding.

[bandersen]

Wow, the original 6BK4 shows no signs of browning from x-rays. Seems to confirm this is a low hour set.


Here are some heavily used ones for comparison.

[bandersen]

Kind of Mouser to take such good care of this lone capacitor.


I'll work on the chroma and IF boards in place next then move on to the chassis mounted components.

[Electronic M]

Originally Posted by bandersen

Kind of Mouser to take such good care of this lone capacitor.


I'll work on the chroma and IF boards in place next then move on to the chassis mounted components.

I think mouser has some kind of code on how to pack something based on how many there are. I'll order a bunch of different film caps and sometimes they'll be in the price break order of 10, sometimes I'll order 12, sometimes I'll order 100 ....If they come in 100 from Panasonic I'll get a Panasonic bulk bag, on qty 10 I'll get a normal mouser ziplock, on qty 12 they'll fold the ziplock funny and staple it or tape the end shut or some other goofy nonsense that makes the ziplock harder to reuse (which I usually do). I've seen different methods used for different odd number parts in an order too so I think it's some kind of nemonic used by the packers to check themselves...

[Videotechie]

So I'm chiming in to ask a question . ONCE restored are these Ctc5 somewhat reliable. I had a ctc4 a while ago and the color sync circuit kept failing restored. I asked the te h if they can improve the circuit with better restore and or caps. Fixed set and didn't respond on any possible upgrades tried on circuit. Ran set once in a while and same circuit failed. Just got rid of it since not a reliable watcher.

DOES anyone do any engineering or reliability upgrades to improve run times in hours of these sets. Those sockets look pretty crispy.

If I was ever to get an old color tv, ways to maximize uptime in hours running. If I had that set, I would readily change out those plastic sockets for ceramic. These sets produce tons of heat. Does anyone run their old tvs with cooling fans ??

I guess those sockets look OK, might be pict HV tube got toasted..

[bandersen]

I've never owned a working example before, but I've heard from others they are finicky. The convergence is difficult and potentially needs to be done every time you move the set around due to the Earth's magnetic field.

Cleaning up beautifully


Also started digging into the flyback area.



I wonder if this is what took the set out of service? All tubes are RCA branded and many are originals.


Found an old service tag

[Electronic M]

Originally Posted by Videotechie

So I'm chiming in to ask a question . ONCE restored are these Ctc5 somewhat reliable. I had a ctc4 a while ago and the color sync circuit kept failing restored. I asked the te h if they can improve the circuit with better restore and or caps. Fixed set and didn't respond on any possible upgrades tried on circuit. Ran set once in a while and same circuit failed. Just got rid of it since not a reliable watcher.

DOES anyone do any engineering or reliability upgrades to improve run times in hours of these sets. Those sockets look pretty crispy.

If I was ever to get an old color tv, ways to maximize uptime in hours running. If I had that set, I would readily change out those plastic sockets for ceramic. These sets produce tins of heat. Does anyone run their old tvs with cooling fans ??

I guess those sockets look OK, might be pick HV tube got toasted..

As someone who has owned and fixed every RCA roundy color chassis (except the CTC-12) I can tell you that if you want a reliable regular use set shoot for a CTC-7 or later. The CTC-7 was RCAs first chassis to use the modern convergence and chroma demodulator circuits that they stuck with until the end of roundys. The CTC-5 and earlier they were experimenting with different circuits because what they had was either too expensive or not sufficient in performance...the CT-100/21CT55 was on the expensive end, the CTC-5 was on the insufficient performance end (they cost reduced it so bad they backtracked on the CTC-7). If you have your heart dead set on something older than the CTC-7 my recommendation would be the 21CT55... It's basically a CT-100 factory modified to drive a 21" CRT (and you can make any 21" roundy color work with minimal tweaks to the set) so it has the engineered for best possible quality model 5 NTSC committee demonstration chassis that sold the FCC on all electronic color. I run my 21CT55 somewhere between daily and monthly and have done so for over 5 years now with minimal maintenance....the downside of the 21CT55 is rarity (there's around 40 in existence) and expense...I paid nearly 2k for my set in unrestored barn find condition, and they use a TON of caps including needing the expensive doorknob HV caps changed (I've worked on 2 of these chassis and both either came to me with shorted doorknobs or developed them after some use), and the general complexity of the chassis makes for More general parts replacement than most.

[bandersen]

More progress in the HV area


It sure looks like this is a crude old replacement.
That added 56K resistor leads me to believe the pot is not quite the right value. Will investigate further.




I was able to remove the HV box rust while preserving the labels. I then clear coated with poly.

[bandersen]

The focus control should be 200K rated for 1W.
There's an Allen Bradlay 2W mil spec Type J pot in there. The resistor is not original.

The pot next to it is horizontal centering while the 3-pos switch is width.



I can't make out a value. I think that's a part# stamped on it. Seems to measure about 150K across.


Boy they sure did tinker with this design.

[bandersen]

How often do you see a resistor with a violet multiplier?
This 100M resistor sets the bias on the 6BK4 HV regulator tube.
None of my meters go that high directly, but I can put my Fluke 27 in nano Siemens (conductance) mode where 1nS = 1,000M.
This allows measurements up to 100,000M ohms and it is off as are the associated 1.8 M resistors.


Luckily, 100M resistors are still readily available.

Now, this is a simplification of the HV circuits used in the chassis that came before and after. They used fixed resistors in place of a HV control.
It's been recommended by EM that the circuit be modified and a control installed like the ctc-7 chassis.
That's detailed in this thread. I will do that once (if) I get this set actually working.
https://antiqueradios.com/forums/viewtopic.php?t=425833

[old_tv_nut]

Wow. Makes me wonder what kind of material the original 100 M was made of.

[bandersen]

Here's a good article from Sylvania on the shunt regulator: https://www.worldradiohistory.com/Ar...-News-1967.pdf

I see now how it works. It's not so much a fixed voltage regulation set to a reference as it is a constant voltage regulation by load balancing between the shunt regulator and CRT beam current.

That variable control sets the operating point. I've heard from a number of owners that these CTC5s suffer from low HV and adding an adjustment helps.

Not much to do on the IF board. Note the germanium detector diode in the lower right.


I wasn't going to remove this board, but it was just too darn dirty.
It has a delay line and funky three-legged part on the underside.

[Videotechie]

Great pics banderson. Electro M Great info! Your knowledge is extensive. I'm glad to see some upgrading to some solid state parts. While not being a purists. More uptime views than on bench makes these more feasible.

It's ironic your signature Electro M. I had a 25mc33 or something similar zenith rounds. Didn't keep but should of. Cabinet was good old fashioned particle board. But the tv was a great performer and nice picture.
Have not seen another zenith roundy near me since.