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Mod to prevent cathode follower arcing on startup

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  • #16
    Originally posted by mikepukmel View Post
    Thanks, Catalin. So, this arcing really is a warmup issue. Once the CF is warmed up, and conducting, when the standby is turned off, even if the HV is higher than normal by 20-30v, it might not be enough to cause an arc. Id love to build a test circuit, and put increasing HT on the grid, and see what happens when the standby is turned off, and at what point (if any) an arc would occur, with a warmed up, conducting tube.
    Someone consider a hundred volts as a safe limit. For this reason a diode or neon bulb will work. As time the voltage drop below 90v it will be blocked so in fact is out of circuit.
    "If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."


    • #17
      the cathode follower has a tendency to arc.
      As you speak of arcing: Has anybody really seen an arc?
      I think arcing at a "lowish" voltage of 450V or so would mean poor vacuum. Which tube brands are concerned?

      I re-read Nick's thread on DCCF failures and found no indication of arcing between any electrodes. (Hope Nick will chime in).
      - Own Opinions Only -


      • #18
        I have no expertise to add, but I will say that there about a million JTM45s out there that aren't having any problems with the stock circuit. You don't need to fix a problem that doesn't really exist.