Postwar American Television
RCA CTC-5 Restoration
By Dave May
May 12, 2012
I set the chassis up on my Telematic test rig. I did need to make a yoke adapter. This was not a problem. I began the soft start at 50% power and very slowly raised the voltage. My volt meter was tied to the top cap of the horizontal output tube (removed from the tube). At about 60%, I started receiving sound. This confirms the tuner, IF section and audio were working. After I reached full power, I removed the voltmeter and reattached the cap to the hor out. Upon powerup, the high voltage attempted to come up. I then shut things down.
This set wil need a full recap. All paper caps and electrolytics will be replaced. I will restuff the cans if the replacements will fit. Otherwise, I'll gut the cans and hide the replacements underneath. Once I recieve the parts, I can proceed.
May 25, 2012
I completed the recap. There were some issues. The vertical was flatlined. One of the caps I replaced was connected incorrectly. The vertical oscillator tube socket had a broken pin connector. I replaced the socket. That initially did nothing but get that tube to conduct (it wasn't before). After retracing my steps, I discovered the miswired cap. Once I reconnected it, the vertical returned to somewhat normal. The 6BQ5 (vertical output) was very weak. Replacing it got me a nearly full screen. I thought I had a linearity problem. I still don't get full screen. Then, I looked at the print. The yoke's resistance reading on the vertical coils was 60 ohms. The resistance on the rig's is 20. I think this difference is the reason the rig doesn't show full screen.
My high voltage was low, about 16Kv. With the top cap on the 6BK4 removed, it went to roughly 22KV (as specified in the print). My voltages on the grid and cathode of the regulator were identical. The print showed 410 on the cathode. The print also showed a test jumper. I disconnected it and the HV went to about 20KV. The grid and cathode voltages on the 6bk4 returned to normal. I think the rig yoke's resistance may play a part here. I have excessive width (same symptom of all other round screen sets I serviced on the rig). I think everything will be back in spec when I return the chassis to the 21AXP22 and its proper yoke.
With the high voltage and vertical working, I could confirm the rest of the set was working. I did find some hack repairs. A resistor and cap were added to the contrast circuit, as well as an additional electrolytic. I removed these extra parts and returned the circuit to print specs. The color looks good. The flyback runs cool. The picture on the rig isn't the greatest. I think it will look much better on the metal tube. The next update will be when I return the chassis to the museum.
May 19, 2013
I returned the chassis to the museum and reassembled the set. Upon powerup, I can confirm that there is no issue with the vertical filling the screen (it was from my rig). I began setup with greyscale, convergence and purity.
Getting the convergence looking good was not fun. Unlike on newer sets (like a CTC 9) the red and green converge seperately. After getting the convergence to a point where the set was watchable, we had a decent color picture. The convergence was not perfect and neither was the purity.
I also need to note that the vertical output tube is a 6AQ5