Belated report on a mishap which occurred August 6, 2025, followed by recovery. This post, November 5, 2025.
Update, August 10, 2025
On August 3, 2025 I heard a snap sound while watching the CTC-5, but all appeared normal. The set continued to work well the next day and on August 6, 2025 about 1 minute after power up, we lost raster 100%, but we had sound. No smoke, no odor. An anxious call to Mike ensued. The following is from Mike.
Greetings Marshall. Since my return on Aug. 3rd to attempt and finally fail to do a repair there, the chassis has returned to the bench at my home. While at the house on the 3rd of Aug, a 3/10 amp flyback protection fuse was found to be blown. You reported several loud snaps prior to the loss of raster on the set. The source of those snaps is still unknown but the suspicion is that there was an arc from the top of the 6BK4 regulator tube which previously during all restoration processes, the H.V. top cover was removed and not installed until the day I returned the chassis on the 20th of July. After replacing the fuse and all of the sweep tubes, I only had weak H.V. (about a kilovolt). And the filament on the 3A3 rectifier could not be seen an illuminated. That is when I decided to return the chassis to my bench for further testing.
The first thing that I did was install solid state rectifiers in place of the 3A3 H.V. rectifier and also on the 1V2 focus rectifier. This restored the raster but not with full screen width. About 2 inches short on left and right sides. I also noticed that there was no control over the H.V. by way of the pot that I installed during the restoration. This was corrected by replacing the 6BK4 regulator tube. I now have control over the H.V. I suspect that this tube failed and caused the arcing within the cage but I will never know for sure about the sequence there. No way to know. I have done a number of tests througout the Horizontal sweep circuits and my conclusion is that the flyback has several shorted turns in the primary winding which is causing lack of full sweep and also lack of enough current to supply the filaments of the 3A3 and 1V2. All of the resistance values of the flyback are within range according the the Sams Photofact documentation but a few shorted turns of the very small wire of the primary which normally measures 450 ohms, would be impossible to detect since when the documentation was done sometime in 1956 or 57, digital meters had not yet been invented so precise resistance is only rough for us at the 450 ohms.
Since all other parts of the sweep circuit seem to be OK, I will be installing my one (and only) spare flyback sometime in the next couple of days. I hope that it is a good spare. The only way to know is to install it and see what happens. I will be monitoring flyback current when first applying power.
This is where we both say a “Hail Mary”
Cheers, Mike
Update, August 11, 2025
Greetings. The operation was a success. The patient lived. Normal H.V. 21KV (and adjustable). Full sweep and good focus. Flyback current is 220 ma. Same measurement with failed fly was 300ma. All good now. I will cook for a couple of days but for short periods and only at night with this heat.
Cheers, Mike
Update, August 13, 2025
I have cooked the chassis several more times today. All looks good. Before I changed out the transformers, I used my digital ohm meter to compare the primary transformer resistances in order to further prove that the transformer had failed. The proof was there. The failed unit was 466 ohms and the replacement unit was 491 ohms. So, there is a 25 ohm difference which means a short in the winding. I decided to open up the top of the H.V. cover with 2 big holes for ventilation. It should not compromise any safety issues with fire. After about an hour of operation in the shop with the temps at 100 degrees, the flyback was only warm to the touch. This is a very good sign. Also, the width control switch is now a minimum width instead of maximum width. It is a 3 position switch that selects different windings of the flyback for sweep width. Also a very good sign. My last evaluations of the flyback failure is not only due to the failure of the H.V. regulator tube, but more of long hours of continuous operations in hot conditions. It very likely would have failed very soon anyway. The Sams Photofact calls it out as 450 ohms. Back then, only analog meters were used for this type of documentaion. The RCA print does not call it out at all. As a point of reference here, I am including more numbers for the flyback. RCA printed what was known as the “drawing numbers” on almost every part. Those numbers are different from the actual part number. So, if we go surfing on the internet for a transformer, both numbers need to be known and displayed. Here they are:
RCA Part number is 102132
RCA Drawing number is 1106255-1
Pix 1 Failed flyback on left and repalcement on right.
Pix 2 Same with other side view.
Pix 3 Modification for H.V. cover.
Update, August 17, 2025
Mike came to the rescue and returned the CTC-5 chassis with a replacement flyback transformer from his donor chassis and all is well. The contrast is better with the new flyback and Mike noted that the horizontal sweep control is set at minimum range which is an indicator of a stronger flyback. He said the old flyback that failed, had the sweep set to maximum to sweep the horizontal raster.
One week later, August 24, 2025.
New screenshots and a video clip from Wizard of Oz. We compensated Mike well for the restoration and I’m grateful for his generous donation of his personal back up flyback for his CTC-5. Now on hunt for a CTC-5 donor flyback to pay it back.
Tap on below image to watch a brief video from Wizard of Oz on the RCA CTC-5.
https://videos.files.wordpress.com/Y...s/mah01896.mov
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