[UK-CONTEST] Cooler is better

[Paul Beecham]

Hi all, I run 2 Acom 2000's and in the heat of battle the shack soon heat's
up. Instead of installing  auxilliary fan's I've put 2 shower fans in the
cavity of an outside wall at floor level and put the amp's air inlet
directly behind them. They run really cool and get a constant suuply of
fresh air. This of course won't suit all applications but it's good for me!
pictures of this at
http://g6pz.magicbug.co.uk/gallery/Shack-Photos?page=1  73 Paul G6PZ
----- Original Message -----
From: "G3SJJ" <g3sjj at btinternet.com>
To: "UK Contest Reflector" <uk-contest at contesting.com>
Sent: Monday, October 10, 2005 10:47 PM
Subject: [UK-CONTEST] Cooler is better


> 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.
>
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