On Sun, 10 Jun 2012 18:59:41 +0200, Antonio I0JX wrote:



The tube manual reports that the absolute maximum plate voltage for
6F6s is 375V. So, designing a receiver with 380V on the plates does not
seem to me a good engineering practice. I guess that the 6F6s will
become very hot, but evidently they shall survive.


The tube manuals that I have declare that their ratings are "average
expected values" or something like that -- basically, they are numbers to
be followed when your set is plugged into the wall and the line voltage
is 117VAC (or 110, depending on the year), but they are not ratings which
will lead to immediate and catastrophic failure if they are exceeded.

Tube failure conditions to not have as sudden an onset as semiconductors
-- so industry practice was often to sneer at the tube ratings as you
passed them by, and accept a lower tube life in return for a less
expensive set.

Lowering the supply voltage to those tubes will reduce the maximum audio
power a bit and let the tubes run cooler, which will make them last
longer. Since you can no longer schlep down to the local five and dime
to get tubes cheap, that may not be a bad idea.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com