On Mon, 7 Apr 2008, Chuck Harris wrote:

A wrote:


Which means by simply lowering the lamp's applied voltage by 5% we
increase
its life by nearly 2 times!

Yes, and sometimes it is worth doing this. I'll bet that the long life
bulbs out there are made with a little more filament wire so the
temperature is maybe (also) 5% lower, too.

Which fits very nicely with the wartime conservation recommendations made
by some of the tube manufacturers.

Fine.

Now, the second part of the question is: does it matter?

If the filament life under normal operating voltages exceeds 20,000 hours,
than dropping 5% and gaining an additional 18,000 hours, is probably
not going to result in a noticeable improvement in life. Forever is
forever.

FYI, FWIW...

Well, that is, kinda, why I was trying to bring the discussion FROM the
"manufacturers recommendations" (on large populations) TO what is everyone
noticing from their own (multiple) amplifier experiences and what everyone
else yaks about in terms of their own (multiple experiences) with filament
power tube lifetimes.

Yeah...20,000 hours is a whole lot of ragchewing. I think I never in my
life spent more than about 10-15 hours/week with amp filaments lit up.
Today, I have the 813 filaments on about 2 hours a week (and drive the
pair with a single 811 in gg and it's filament is on, also, and not
not voltage managed, either). And, I've never blown an 811 filament, ever,
and I had a few of those tubes in amplifiers, too.

FYI, FWIW

-Chuck Harris