RCA CTC-5 Deluxe Chandler Restoration

[Penthode]

Originally Posted by trinescope

My 5, although basically working, could probably use a wholesale replacement of the carbon resistors, since I've already had so many of them that were either off value when I started, or have gone bad over time and caused new problems. My HV probe is a Fluke, and the kind used with an external DMM, and seems to be accurate. The big issue is how the HV just drops off suddenly if the brightness control is advanced too far, and, according to others here on this board, is a normal characteristic of the CTC5. In any case, IMO, the 5 really isn't a good "daily driver" because of the weak HV supply and the fact it just isn't very bright with the original AXP tube, not to mention convergence drift with the DC static adjustments instead of the magnets everything else used.

I use the CTC5 regularly and it delivers excellent color pictures. The Deluxe Chassis has wider bandwidth Chroma demodulation so it provides a bit more color detail.

The HV drooping issue was a concern which was mainly addressed by selecting a new horizontal output tube and replacing the vacuum tube HV rectifier with a solid state replacement.

Two issues I see is the dimness of the 21AXP22 which is overcome watching the set in a darkened room. The other is poorish black level clamping which I feel may have been exacerbated by the contrast control modification.However I do not see it any worse than subsequent chassis's CTC7, CTC9 etc.

[old_tv_nut]

Regarding poor DC coupling, I am torn between keeping it authentic or making it better than original. So far I have come down on the original side, a good part because I'm lazy.

[Penthode]

Originally Posted by old_tv_nut

Regarding poor DC coupling, I am torn between keeping it authentic or making it better than original. So far I have come down on the original side, a good part because I'm lazy.

I suppose you noticed it too? It is not too bad but is noticeable at the opening and closing credits of a program when high luminance change actors appear and the background it overlays dims. The original contrast control which was a degenerative DC bias control vs the modified variable AC cathode bypass I think provided better dc coupling. Its downside was the uncomfortable interaction between brightness and contrast. However the original circuit I believe also provided the proper dc reference to set best gun tracking. I do notice this set is difficult to get consistent tracking due to the way the luma feeding the matrix is derived. Could open another thread to discuss this. I feel I see the problem and haven't bothered to come up with a good solution

[old_tv_nut]

I did put in the CTC-7 circuit change, my excuse being that was something actually being done to sets in the field. No sets had 100% DC coupling after the CTC-5 until some point when it was done in transistor sets. Consumer Reports complained about it every year.

[etype2]

Some progress.

After a Summer break from the hot Arizona heat, restoration resumes.

September 20, 2024, Day 138

From Mike. I am slowly changing parts on the Sound, AGC, Sync printed board. I have found a number of questionable solder connections along the way on this board. It has forced me to change every single component except for the transformers which are typically not problematic. Somebody missed "solder skills day" in the process of manufacturing. I think this set was very problematic from the day it left the factory. Obvious bad solder joints with component pins easily seen moving when exercised from the top of the board. Also, I found some notes in my CTC5 "red line" drawings that reminded me of a mod that I made on my set in the High Voltage Regulator. I added a HV control. I will be doing that mod on this set. It entails removing a control on the back panel that never did anything. It is called the Matrix Balance control. It is supposed to control current in the "X" and "Z" demodulator tubes by way of adjusting cathode current. This is the only RCA color chassis that ever implemented that control and it was eliminated. All sets after CTC5 used a fixed cathode resistor, which is the best way to go. I will replace that control with a 10 Megohm pot and a resistor divider in the HV regulator tube circuit to allow for HV adjustments.

More to come. Cheers, Mike

[etype2]

September 25, 2024

Update for AGC, Sync, Audio rebuild

The printed board that controls AGC, some of the Sync and all of the Audio has been completely rebuilt. I replaced all of the components on this board, not just the capacitors. I found some resistors out of tolerance and a number of cold, poor solder joints throughout. This board was no doubt causing multiple intermittent problems for many years, one of which I experienced earlier in this restoration. There was a horizontal sync problem that mysteriously went away. I decided to do a complete component replacement as opposed to looking for intermittent solder connections and/or faulty components. The CTC5 had numerous issues with AGC and most of that is due to the fact that the engineers thought that it was a good idea to create the 140 VDC power source from the cathode of the audio output tube. VERY BAD design to mix any two circuits that way. I do not know why they did not just add a 20 watt resistor to the existing 285 volt supply which would have been a better design. It would have been a very robust design compared to making the audio output tube do the work of making the 140 volt supply which caused many problems that were difficult to troubleshoot.

Pix 1 Board before restoration.

Pix 2 Board after all components changed.

Next, I go to the High Voltage Regulator and make a mod to allow control of the High Voltage setting.

Cheers, Mike

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[jhalphen]

Hi to all,
Hi Etype2,

Following this restoration's progress with interest.

Will you use the CTC-5 through it's RF tuner or add a video input for better resolution?

An idea of when it will be completed...

Best Regards
jhalphen
Paris/France

[Penthode]

Originally Posted by etype2

...The CTC5 had numerous issues with AGC and most of that is due to the fact that the engineers thought that it was a good idea to create the 140 VDC power source from the cathode of the audio output tube. VERY BAD design to mix any two circuits that way. I do not know why they did not just add a 20 watt resistor to the existing 285 volt supply which would have been a better design. It would have been a very robust design compared to making the audio output tube do the work of making the 140 volt supply which caused many problems that were difficult to troubleshoot....

On the contrary, it seems to me a very good idea to use the output tube to divide down the B+ to 140vdc. It is better than using a dropping resistor because the output tube regulates the supply. A dropping resistor would mean the voltage would vary widely since it would be load current dependent.

[etype2]

Hi Jerome,

Mike did not make that modification for our previous restorations, so I doubt it will happen on this set. Is there a visible improvement by doing this? I’m in the camp for leaving it stock.

Completion, possibly by the end of this year?

[jhalphen]

Hi to all,
Hi Etype2,

Video input mod will not yield "spectacular" resolution increase except if the tuner and especially the IF chain has drifted badly out of optimum bandpass.
I suppose your Golden Restorer will do a full RF/IF sweep on your set.

As a personal experience, on my CT-100 i purchased Pete Deksnis's video input kit - derived from RCA's studio monitor mod (about 20 years ago). The seller of my CT-100 warned me that the TV was not performing very well on upper VHF (Band III) channels.

As the CT-100 requires IF alignment of no less than 5 IF stages, i chickened out. It is one of the most difficult sets to align and you need a full Lab of gear to do it.

The CT-100 video input module works well, but as you know from your Westinghouse, the 12" picture of a 15GP22 is nothing to brag about resolution-wise.
Oh well, it's IN COLOR ! (1954).

Best Regards
jhalphen
Paris/France

[Penthode]

Originally Posted by jhalphen

Hi to all,
Hi Etype2,

Video input mod will not yield "spectacular" resolution increase except if the tuner and especially the IF chain has drifted badly out of optimum bandpass.
I suppose your Golden Restorer will do a full RF/IF sweep on your set.

As a personal experience, on my CT-100 i purchased Pete Deksnis's video input kit - derived from RCA's studio monitor mod (about 20 years ago). The seller of my CT-100 warned me that the TV was not performing very well on upper VHF (Band III) channels.

As the CT-100 requires IF alignment of no less than 5 IF stages, i chickened out. It is one of the most difficult sets to align and you need a full Lab of gear to do it.

The CT-100 video input module works well, but as you know from your Westinghouse, the 12" picture of a 15GP22 is nothing to brag about resolution-wise.
Oh well, it's IN COLOR ! (1954).

Best Regards
jhalphen
Paris/France

I not only had to align my CT-100, mine had a mouse nest in the video IF area and I had to fully diassemble the video IF stages, use an electrolysis bath to remove the corrosion and fully rebuild it.

The equipment I used was the HP8601a Sweeper Generator I bought for $40 (I just picked up anpther one last week for less). Plus an HP8600a Digital Marker. The HP combo was designed specifically for this sort of work and provides five absolutely accurate markers. Plus I needed my trusty 40 year old Hitachi scope (which I got for free). I made the input jig RCA specified and used a genuine RCA bias box I found in a pile of electronic garbage years ago.

The alignment was pretty easy and ultimately the results matched exactly the RCA notes. The only issue I had was alignment of the 1st IF tuner link. An open decoupling capacitor in the tuner fixed that. I believe the decoupling capacitor is a common problem and overlooked. Once fixed the process was easy and results exactly as described. The resultant pictures on the 15GP22 are phenomenal... that was before the convergence transformer failed. I will have time to return to that again this autumn. It is all explained in the link below.

You don't need special laboratory equipment. Simply a good nose for a bargain and there are literally plenty of equipment bargains about. I still highly recommend the HP8600a/HP8601a combo because they are relatively cheap and produce the highest quality alignment results.

Here is the link which includes the process of my CT-100 using the HP equipment. Look at page three where the Video IF section of the CT-100 is in the bucket of water indergoing electrolysis rust removal. If this CT-100 can yield a perfect IF response, then any CT-100 can.

https://videokarma.org/showthread.php?t=274959

[etype2]

Jerome,

Mike will do a full alignment. Is your CT100 working?

[etype2]

UPDATE, November 24, 2024

Greetings Marshall. I started looking at the CTC5 again this evening and I will be attacking the H.V. regulation modifications next. The plan is to install a H.V. adjustment control in place of the Matrix Balance control which is located right next to the 6BK4 regulator tube socket. The Matrix Balance control never worked on any CTC5 that I have ever worked on. Every chassis that followed the CTC5 did away with it and replaced it with 470 ohm resistors at the cathodes of the demodulator tubes, and that is what I will do here. The pictures attached are as follows.

Pix 1 The parts that came out of the AGC, SYNC, Audio I.F. board from the last update. I missed sending it at that time.

Pix 2 is the 6BK4 Shunt Regulator socket. Notice the control on the right side with a yellow and blue wire. That is the Matrix Balance control that I will remove. In place of it will go a 10 megohm pot that will allow control of the H.V. regulator. I have already disconnected those wires on the other end where they connected to the demod tubes. Since this modification causes changes in the Chroma circuits, I will be doing the component replacements in that section next instead of moving to the Vertical sweep section. I did a random "in circuit" check of resistors in the Chroma section and there are a number of resistors that are out of tolerance by over 20%. So, that will be a slow task since it is all hand wired. One more note. The H.V. as measured at this point in time before mods is 17 KV. I hope to be able to adjust between 19KV and 22KV if all goes well.

More to come, Stay tuned!

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Good evening. I have made some progress over the past few days. The H.V. Regulator circuit has been modified. A H.V. control now exists and the H.V. can be varied from 16 K.V. to 23 K.V. I have also decided to eliminate the 5U4 Rectifier tubes in the power supply and replace them with a plug in solid state replacement of silicon rectifiers that are rated at 1000 PRV at 2.5 amps. These plug in replacements can be purchased, but I make my own from old dead 5U4 tubes. I break away the glass and save the sockets and install the 1N2007 rectifiers into the socket which makes it plug in directly to the where the tubes were. These rectifiers take the place of both 5U4 tubes for power handling capabilities. The improvement is power B+ stability throughout the chassis and it saves 6 amps of current not being handled by the power transformer to power the filaments of the 5U4s. Since the solid state rectifiers are more efficient, the B+ increases by around 30 volts so I installed a 70 ohm 50 watt resistor (chassis mount type for heat control), to the top of the chassis where the 5U4's were. Now, on to the Chroma circuits. First thing I noticed is a very badly charred terminal strip where a 10 watt resistor mounts. I remembered this from my own set and it is weak spot that needs to be addressed. The charred terminal strip eventually turns in to conductive carbon and if it doesn't disintegrate first, it can actually cause a small fire. This is a very delicate piece of surgery and the 10 watt resistor that caused this damage will be re-mounted to the top of the chassis where it can dissipate its heat away from the chroma circuits. Very bad design on the part of RCA in my opinion. Basically it is a 10 watt resistor in a 15 watt circuit. I have also installed a 5 amp pigtail fuse in line with the power transformer primary. That should have been done by RCA in the beginning.

Pix. 1 H.V. reg 6BK4 socket before mod.
Pix. 2 H.V. reg 6BK4 socket after mod with H.V. adjustment added
Pix. 3 H.V. adjustment set for 16KV
Pix. 4 H.V. adjustment set for 23KV
Pix 5 5U4 tubes with solid state replacement at the bottom of the pix.
Pix. 6 Chroma circuit with charred terminal strip. Hard to see from the pix.

I will send pixs in 3 separate emails. I hope it goes well.

cheers, Mike

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The chroma terminal strip will be a very slow and delicate piece of surgery. Lots of wire and re-locating of parts to get the heat away from the chroma circuits.

Cheers, Mike

[etype2]

Small update.

Mike,

Excellent work! Looks like we will have good HV regulation.

Peace,
Marshall

Yes, the H.V. regulation is good. And, I can change it from 16 KV to 23 KV if I want to for best sweep and focus.

Tonight I was looking at the chroma circuits a bit and noticed that the R-Y, B-Y and G-Y tube sockets need to be replaced. They are very brittle and have intermittent tube socket connections from many years of heat from the tubes. More on that later.

Cheers, Mike







[etype2]

December 9, 2024

Update.

Greetings. I have done many things on the restoration since my last report. A lot of time has been spent on the restoration of the Chroma Circuits. What a mess. But first, let me recap on the last report with details. The first picture will be of the mods in the power supply. Top of chassis showing the two 5U4’s removed and replaced with 1 “plug in” using solid state 1n4007 rectifiers. Also, along side is the 70 ohm 50 watt chassis mount resistor to take care of the increased voltage that resulted in the mod. I also replaced a dual potentiometer for the red/green dynamic convergence. No picture for that. The green section was beyond cleaning. I had a good spare unit in my CTC5 Junk.
OK, now to the Chroma Circuits. There have been a number of things to address. One, problem was that the gray scale changed every time I fired up the chassis. Then it would slowly change from red, to green, to blue slowly, then any color and back again. This usually resembles a failing CRT, which is not the case here. I traced this problem to the tube sockets of the R-Y, G-Y, and B-Y / Blanker tubes. (12BH7’s). The filaments were changing in brightness. It was necessary to replace both of those tube sockets. The gray scale is now stable. Another issue with the Chroma rebuilding was a failing terminal strip. In the picture, this can be seen above center in the full view photo. Also shown close up in another photo. The terminal strip overheats due to a big 10 Kohm 10 watt resistor that never should have been installed there. I have moved it to just above the chroma circuits, and away from the sensitive tuned coils. It can be seen in the full view photo just left of center. It looks like a cement rectangle. In the later photo, it is missing because I moved it out and away from the Chroma Circuits. and you can see where I replaced a burned wire with a new white wire. I replaced a lot of resistors that were way out of tolerance, and of course all wax type capacitors.
Photo 1 5U4 tubes removed and solid state rects installed. Also, 70 ohm 50 watt resistor chassis mounted for heat dissipation.
Photo 2 Chroma strip charred
Photo 3 Chroma Circuits b4 component upgrades.
Photo 4 Chroma strip replaced
Photo 5 Relocation of the 10 K ohm 10 watt resistor
Photo 6 Replacement of the 2 tube sockets bottom view
Photo 7 Replacement of the 2 tube sockets top view
Photo 8 The Chroma Circuits finished with rebuild
Photo 9 All the components that I replaced in the Chroma Circuits.
Photo 10 CTC5 Color pattern when finished with Chroma Circuits.

Next is the Vertical sweep board.

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