Quote:
Originally Posted by Tubejunke
I am just curious as to how this aspect panned out for you. I am working on a similar vintage Zenith and your findings are almost identical to what I was finding in my set except I can't get 190mA. More like 200 or maybe 210 at 110V. My flyback seems hotter than I would like it to be after about 30 minutes of operation. I am waiting on a replacement socket for my HV rectifier which was burned up and the 1W resistor was open (blasted in two).
I had long been searching for the source of a very light HV hissing that was intermittent. It couldn't be seen down inside the insulating cup of course. I think that we should be able to achieve correct cathode current at full line potential. Like you, I used a variable source to control this, but I don't think it would be necessary to use that or alter the line voltage in a healthy set. Also, I found that just having the raster fill the screen is not guite all my set needs. The higher line voltages (above 110V) around 115V or up give a much crisper or clearly defined picture once video comes into play.
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You may also want to check the cathode current of the 6BK4. The Sams for my set says to adjust the HV to 24kV and make sure it is at least .9 mA. If I recall right, mine was about 1.9 mA with 24 kV. The schematic showed a 25-26 kV voltage and the 21FJP22A spec has a maximum rating of 27.5 kV. I adjusted my HV for 25.5 kV. I noticed that my HO cathode current went down with the higher HV setting. Maybe you can reduce your HO current by raising the HV, if your CRT and set will permit it.
Dave