On Tue, 8 Apr 2008, Chuck Harris wrote:

A wrote:

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

If we extend the universe of tubes observed to the TV and radio types, I
would have to say that it is very rare for me to find a burned out filament
in the 6.3 and 12V tubes. And very common in the very delicate 35-75V tubes
used in series string sets.

-Chuck


Well, my comparable experience is the ac/dc AM/FM radios (12 v and 35 v
tubes) and in another post I mentioned buying up a number of them at a
couple of hamfests (and a thrift store) and finding that they all still
worked AND had the original tubes (marked with same brand as brand of
radio) in them.

But, the series string strategy was obviously the "cheap" way for
manufacturers to save on the price of a power transformer AND any
irregularities in the filament mechanical tollerance contributed to early
failure, which, of course, contributed to pressure on the consumer to buy
a whole new TV or radio, thus contributing to the nation's economy (if you
get my drift).