EL84 variety and screen grid glow

Mainstream EL84s are supposed to operate in a standard class A mode (Ua =
Ug2 = 250V, Ia = 48mA) at about -7.5V bias. I believe, 6BQ5s should do the
same.

"Old reliable" Soviet 6P14P, similar to EL84, reached the same working
point
at about -6.5V...-7V bias.

However, a new Russian "Sovtek" 6BQ5 tube I purchased needed -9V bias to
run
at the same standard operation point. I am wondering why the difference so
great (20%)? Is it just a faulty tube? I also noticed, looking inside the
anode box, a strange orange glow on the screen grid. It was not because of
excessive dissipation on the grid (Ig2 was only 5mA). It was *not* a
reflection of a cathode glow -- much brighter and more yellowish than the
cathode.

The screen grid glow was only on the inside surfaces of the grid wire,
facing cathode. It immediately disappears when anode current is shut down.
It looks like a sort of phosphorence on the grid surface caused by the
electron bombardment. It has nothing to do with this blueish glow often
seen
on the inner surface of the anode, which is quite common.

I have never seen (or have never noticed) such screen grid glow before on
any other tubes.

Do you know what it is? And what those Russions have done to the tube?

Regards,
Alex