Recap of the restoration of a RCA 21CT55 without having to read the entire 10 pages of this thread.
The set was fully restored last January, 2017. It took two years and we thank all the VK members who helped and especially Mike Doyle, also a VK member. In July we were doing a video of the 21CT55 and it was running continuously for about 4 hours. We were done and ready to shut the set down. I left the set running alone for no longer then three minutes for a bathroom break 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. I know, first rule, never leave a vintage set unattended. WHAT THE HECK HAPPENED! WHAT LUCK!
After much testing, we thought the flyback failed. The set was only producing 10KV. That was a good sign. More testing with the HV probe and we pulled the regulator tube and found the HV measured 20KV. I can’t remember what the previous voltage was. That led us to suspect a resistor in the HV regulator circuit. We tested it and found it “open”. The suspect resistor was “buried” under the damper tube. This was done at my home and with lack of proper equipment and expertise, off the chassis went once again to Mike’s test bench/shop.
Mike found the open resistor “buried” under the damper tube. He then addressed the color problem I complained about, weak green output. I blamed it on the somewhat tired 21AXP22. It still test “good” but on the low side at cutoff. It tuned out that a simple 1/16 turn CCW of a slug in the L44 Quadrature Transformer made all the difference. The green returned strong and looked good on Mike’s jigged CRT. The resistor was an original (made by International Rectifier) special film type, 3.4 Megohm 3 watt. Mike 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.
Mike let the chassis “cook” (exaggeration) several hours a day for a week. During this time, he monitors the chassis for any anomalies, checks voltages, etc. The HV is 30 KV with the regulator tube pulled. All looked good and the chassis was delivered back to me. We reset the gray scale and did a full setup. We could not get the convergence perfect. Settled for good convergence in the center, top, bottom and left side. The bottom convergence is just as important as the center. Broadcasts usually show text at the bottom. The 21AXP22 looks like a new CRT now. We are happy!
Operational observations: The set comes up with good convergence and seems to reach full brightness in 30 seconds. The image enlarges to a point that after about 25 minutes the annoying Macrovision streaks on the “Gentlemen Prefer Blondes” DVD disappear at the top of the screen.
The cabinet is in good shape but we will refinish the top which has blistering of the old varnish. We still have to polish the brass trim around the CRT safety screen.
Here, a few more screenshots from the 1953 Technicolor movie, “Gentlemen Prefer Blondes”. I’m very pleased with the results.
This link will open an image carousel and full resolution images of the thumbnails can be viewed.
https://visions4netjournal.com/vinta...-carousel-3964
This link will show images from OZ and THE RED SHOES.
https://visions4netjournal.com/vinta...-carousel-3856
If anyone has a copy of the “Service Clinic” booklet for the 21CT55, I’d appreciate it. I checked the ETF and internet. Nothing found. I would like to address the concerns expressed about the HV by several VK members. The resistor failure concerns me but then again, it’s a 62 year old set. Things fail. We can’t replace every single part.
Thanks.