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Old 07-18-2016, 03:15 PM
Ralph S Ralph S is offline
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Join Date: Jan 2008
Posts: 153
TK-31's peculiar spot!

This inquiry is directed to those readers who were active video engineers at television studios in the '50s and '60s and who repaired or ran video on RCA-TK31A cameras.

I've run into a peculiar problem on my '31A which I've not seen before on other similar cameras or on TK-30s. If you look at the attached pictures of off-the-screen shots from my picture and waveform monitors, you'll see a conical spot, dead-center in the picture which is not being produced with either the target or beam voltages "up." (Both controls are at zero position.) This is not a dynode spot. It does not move during alignment of the camera either for geometry or true beam alignment. The only control which seems to have an effect on reducing it is the Multiplier (Multi) Focus control which when turned counterclockwise to minimum, blends the spot into the background (out-of-focus across the screen.)

Some considerations: 1. The camera is equipped with an orbiter coil on the orth section (factory installed) which is not active. 2. The spot has been visible on all 5820s, 5820As, 4401s and 6474s I've tested (a total of more than 20 tubes.) 3. The spot was NOT visible on a Bi-Alkali IO I've tested.
Anyone seen this before and if so, what was the solution?
Attached Images
File Type: jpg 5820 vertical center spot brightened.jpg (42.6 KB, 22 views)
File Type: jpg 5820 vertical center spot on screen.jpg (23.2 KB, 34 views)
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