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12ax7 lights up like a light bulb?


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  • 12ax7 lights up like a light bulb?

    I have some RFT 12ax7 preamp tubes in my Chimera. When I turn the amp on, one of them always flashes really bright for a split second then fades to normal. It sounds good and is not micro-phonic. Has anyone ever seen this? I'm afraid it will mean a short lifespan.
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  • #2
    I had one that did that, but it only did in the PI position. So i switched it out for another one that didnt -though they were both chinese 9th gens.

    Apparently some tubes just do that inherently.
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    • #3
      A couple old RCA's i have in my splawn do that. They sound great so I dont worry about it.
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      • #4
        Some tubes do this. I think it is some current limiter thing built inside them.


        • #5
          Dunno about a current limiter, but my NOS valves seem to do it more than current production.
          It can be pretty scary seeing a


          • #6
            I have some too. Don't know why they do that. Sounds good so no worry... i call it "prewarm-up".


            • #7
              I have a 6L6 in a Herbert that does that. Only after the amp has been off for a awhile though.
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              • #8
                I have a bunch of Mullards that do that. It's normal.
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                • #9
                  All my Amperex, Mullard, and Siemens 12AX7s do that.

                  Can't remember if my Mullard CV4024 do as well
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                  • #10
                    RFT 12AX7 do this. It's not isolated to the Chimera, that's for sure.

                    Also from my FAQ:

                    "Some preamp tubes also glow brightly briefly on power-up; this can be normal and not a sign of a bad preamp tube."

                    I have some Chinese 12AX7B which do this too.


                    • #11

                      Like that? The video says it's a leaky tube with gas in it.
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                      • #12
                        Sounds like it's time to turn out the lights and invite some girls over