"David Nebenzahl"

What I'm hoping for, of course, is some kewl effect, like
that purplish glow you sometimes see emanating from
the plates of overdriven tubes...

Unfortunately, there's no gas in a "vacuum" tube to glow.

So where does that purplish glow come from? I've seen it.


** The blue/ purple glow is emanating from " impurities" in the glass - it
is generated by electrons hitting the glass at high speed.

Most audio power tubes (ie 6L6GCs, EL34s, EL84s and 6550s ) have cut outs
in the plate structures that allow this to happen.

The blue glow will be there when the tube is new ( if it's there at all )
and is not a sign of a problem.

It may be fairly steady or respond to high drive levels - ie when the
plate voltage nearly doubles in magnitude with signal peaks.


..... Phil