[Amps] Fans for 4cx1000/1500 question

[PAUL HEWITT]

-

Gary Schafer wrote:
>>
>
>Interesting thoughts Ian. Would you
think that pressurizing the output
>compartment on an hf amplifier with a
tube like a 4CX250 or a 4CX1000 would
>be practical?

Just as practical as it is on VHF and
above, where it is the standard
method. The only reason it isn't used so
much on HF is because many
people feel it's OK to let RF wander all
around the insides of HF
amplifiers, so they don't make a sealed
output compartment.

>It sure would help on the 4CX250 if
some back pressure relief could be had.

Certainly would, because that tube is
one of the worst in terms of the
pressure:flow ratio required.

>Looking at that tube though it seems
that most of the air would go out the
>bottom rather than the dense plate heat
sink.

Sure it would  - that's why you have to
*seal* the input compartment and
then provide one controlled outlet. A
hole of 1.0-1.5in diameter (mesh
covered) is about right for two 4CX250s
or similar.

Hello Ian
This may be fine for the 4CX250s and
other "Tiny Tubes" but larger tubes that
dissipate several hundred watts of
filament power may not get enough
cooling air at the base seal.  Verifying
the base seal temperatures could be a
challenge (and or expensive) by only
leaking air into the cathode
compartment.  Eliminating the air system
socket(s) (external anode tubes) and
pressurizing a perforated cathode
compartment and then tank compartment,
(in series and out the anode cooler
last), requires only one exhaust outlet,
making ducting the exhausted air (and
noise) outdoors or elsewhere easier.

There is a nice cooling calculator on
the Kooltronic website that takes into
account inlet air temp and the cooling
requirements of the components the inlet
air passes over, including the blower
motor.  It's much easier to cool
everything with one blower when using an
enclosed cabinet.
Paul

--
PAUL HEWITT
WD7S PRODUCTIONS
QRO HOMEBREW COMPONENTS
http://wd7s.home.att.net