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El84 with voltage on the grid (Simple PP)

I finally got my Edcor output transformers, found a way to install my big M Cap coupling caps under the board. See: https://www.diyaudio.com/community/threads/tubelab-simple-p-p.148694/post-7405838

Now, I was testing different voltages after a couple of hours of listening to it. (sounds really good).
All is good. 325V on the tubes plates, 12 volts on cathodes with 360 ohms cathode resistor.

One odd thing tough: One of the el84 has DC Voltage on the grid. On turning the amp with cold tubes, the voltage will slowly creep up to 1.4 volt after 20 minutes and seems to keep creeping up. Dont know how high it'll get... By the way, there's no voltage on the 3 other tube's grid.
I move the tube to another socket and it follow the tube. The bias stay unmoved at 12 volts. So I guess it ain't the coupling cap that leaking (That what I was thinking first)

Is this a grid leakage on this tube? Should I get another tubes? I use this amp for about an hour a day, maybe two.

Thank in advance for your advices.

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