[UK-CONTEST] Cooler is better

[G3SJJ]

After the Convention Dinner and YOX's superb quiz on linear amps
(disappointed not to have won that!) jut thought Reflectees might like to
see this note from the Acom Reflector. Double edged sword really. The Yanks
did the East a favour by forcing them to make "real" amp tubes with the
downside side of a long wait before you get to the meat!  Chris G3SJJ  :

Interesting to find there seems to be two ways to wire the aux fan.  I
wired mine in - put the wires on the "fan +" and "fan -" solder pads.
The fan never comes on.  Checked the fan - its good.  Checked with Will,
he told me the set point is 80 or 90 degrees C, and set in software and
can't be changed.  I never get to 80 degrees C.

I have one 2000A without the aux fan and one with.  The one with the aux
fan that never runs, runs about 4 degrees C hotter than the one without.
I attribute this to air flow blockage by the non-operating aux fan.

Electronics reliability studies over the years all have pointed up the
fact that cooler is better - the data is compelling.  A few degrees C
however is not significant.  There may be hot spots within the amp that
could benefit from more cooling - but the 2000A seems to be very
reliable from all reports.

The reason there is a 150 second warm-up period is because of the cold
war - no pun intended.  The US blocked the export or thorium related
technology to the USSR - judging it a strategic technology.  As a
result, the Russians did not have thoriated tungsten filaments, and
stuck instead with indirectly heated metal-oxide cathodes.  This is
what's in the Svetlana 4CX800A.  Cathodes take time to heat up to a nice
even dull-red temperature.  If you let the tube emit before the cathode
is evenly warmed up, the hottest spots on the cathode will emit all the
electrons (current), and you can burn a hole in the cathode at those
spots.  The rest of the amp requires no warm-up, but the tubes need a
good 150 seconds.  Tube life may be extended by holding off transmitting
another 30-60 seconds after the timed warm-up, assuming you are not
chasing the country you need to make the honor roll - in which case 150
seconds seems like eternity.  The Alpha 99 timer is 180 seconds.