Update:
We were doing a video of the 21CT55 and it was running continuously for about 4 hours. We left the set running alone for no longer then three minutes and after returning, found the horizontal collapsed about one third of the screen, badly converged color, and out of focus. No unusual sounds or odors present. WHAT THE HECK HAPPENED! After much testing, we thought the flyback failed. The set was only producing 10KV. More testing with the HV probe and we pulled the regulator tube and found the HV was at its full 20KV. That led us to suspect a resistor in the HV regulator circuit. We tested it and fond it “open”. The suspect resistor was “buried” under the damper tube. This was done at my home and with lack of proper test equipment, off the chassis went once again to Mike’s test bench/shop.
From Mike:
Greetings. I installed the new resistor into the HV. regulator circuit and jigged it up tonight. I now have good control of the High Voltage with the adjustment. It regulates between 18 KV and 21 KV as it should. The raster is full, the focus is good and the convergence looks reasonable for being on the jig. You are a lucky man! It appears that the flyback transformer is OK. No photos tonight, it got too late but I will be taking a careful look at the Chroma circuits within the next couple of days to make sure that I have not missed anything, mainly looking at the complaint of lack of Green. Anything is possible at this point since this chassis seems to be full of “surprises” with its early color television circuitry.
Regards, Mike
Greetings. I have done more testing tonight in an effort to identify any issues with the chroma circuitry and paying special attention to the green. All voltages and waveforms looked acceptable. After the testing, the “technician” in me decided to do some “empirical” adjusting of some of the transformers in the chroma circuits. When doing these things, one must be VERY careful to go slowly unless “he” wants to start all over again with the procedures to get things aligned. When I got to L44 ( the Quadrature Transformer), I adjusted the slug out about 1/16th of a turn CCW and the green got stronger on the right side of the raster. All I can say, is, maybe the trip on the road caused the slug to settle a little inside the coil form. This adjustment made no difference in the voltages anywhere but it did improve the green “strength”. All I can say is, “whatever works” and I will not argue with success. This should, I hope, make in improvement in the green response even though the CRT is a bit tired. I have included photos of the resistor I found in the High Voltage Regulator circuit which was causing the reduced high voltage condition and hence the shrunk raster, out of focus and poor convergence symptoms. 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. I replaced it 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. I will be cycling this set for a few days. Please find photos of the resistors and color bars. Please ignore purity issues.
Regards, Mike
Author:
All I can say is the failure was a blessing in disguise. After re-setting the grey scale and doing a complete new setup, the green output is strong now and all the other colors “fell into place” as they should and now look very accurate. It looks like a totally different CRT was installed. Great work Mike and indeed we are very lucky it was only a resistor causing the HV problem. The failure gave you an opportunity to revisit and take a “second look” at the chroma circuits and adjust that slug.
After we improved the color performance of the 1954/55 RCA 21CT55, we wanted to test it against the 1958 RCA CTC-7 Worthington. The 21CT55 uses a 21AXP22 CRT, testing a “weak” Good on emissions and the CTC-7 uses a rebuilt 21CYP22A CRT, testing a “strong” Good. The 21CT55 uses superior “R-Y-Q” demodulation. The following test images are an effort to visualize the differences in image and color quality between a 1954/55 RCA 21CT55 and the 1958 RCA CTC-7 Worthington. RCA 21CT55 images appear on the left series of photos. Tap any image to open the image carousel, then tap the full resolution image tab. All exposures and focus were set at the center of the CRT image automatically by an iPad Pro 2 10.5. This is not a scientifically controlled test, only an approximation attempt with a non-pro camera. Please excuse the reflections.
Go to this link and scroll to bottom of the page. There, you can open the image carousel to view full resolution photo comparisons of each image.
https://visions4netjournal.com/vinta...tv-page-two-2/
CONCLUSIONS?
The first and obvious difference is the overscan of the CTC-7. The color temperatures are close in most of the photos comparisons. Where there are large differences, I believe it to be the fault of the camera. The camera seems to “shift” color temperature on its own. (Time to invest in a better dedicated camera) For instance, look at the fifth and sixth photo comparisons. You will also notice an annoying swath of pale yellow which is causing color variations or discolorations in the photos. This is caused by the camera and not visible when viewing directly. Also, these photos do not do justice to the actual images produced by these televisions. Overall the 21CT55 appears to be adjusted slightly “cooler” and the CTC-7 is brighter. The red gun of the 21CT55 is the weakest of the three.
Wondering why the CTC-7 has so much overscan and whether the overscan can be reduced to match the 21CT55?