extra cooling on the K2

[Ron ZL1TW]

Hi,
      I know it will be said that the K2 doesn't need extra cooling as it
will automatically turn the power down if it gets too hot, but my setup
here might be of interest?
I find the noise of the little fan on the K2 quite annoying, and for some
time now, I have been using a computer muffin fan which I have mounted on a
plexiglass plate that fits over the heat-sink fins, and is located there
with a couple of "keys" that fit down into the fins. There is a hole cut in
the plexiglass panel above the speaker, and I made up a deflector that
"beams" the sound directly at me, rather than straight up. I found this
latter appendage very handy during field day, when the K2 was being used in
a tent, as tents don't reflect sound like home shacks do.
Even a muffin fan can be irritating in a quiet room, and the simplest
solution there was for me to use a series dropping resistor, which works
fine on most muffin fans, but of course, I was stuck with a single speed fan.
The solution was found when I was given a box of "dead" computer power
supplies, and in most of them, the fan had a small PC board attached to one
lug of the fan, with a thermistor that sat against the switching
transistor's heat sink. As the temperature went up, the speed of the fan
increased.
Probably the nicest feature is that the fan runs about 1/3rd speed when
everything is nice a cool and is virtually silent.
I have used this setup for a while now; mounting the small PC board so the
thermistor sits through a hole in the plexiglass, and in contact with the
surface of the K2's heat sink. ( Burying it in a blob of silicon grease
would probably be better....but messy)
The muffin fan will slightly increase in speed after extended CW use, but
the "mosquito like" fan on the back has never come on while using this
contraption.
The PC board has a thermistor with a fixed resistor in series, controlling
the base of a transistor ( part of a Darlington setup with 2 transistors)
which directly controls the fan. Very simple.
I mention this for what it is worth. I find it handy when I use the K2 to
take a CW learners net where text and numbers sent at speed down to 12 - 14
wpm certainly made the K2 heat up. I also like "rag chewing" on the
paddles, so the little fan on the back used to get a work-out. It is super
simple to just lift the panel off when it isn't wanted.
I don't have a web site to post any pics, but if anyone was interested I
could take a low resolution digital pic and send it via EMail.
Cheers.......Ron ZL1TW

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[Peter Linsley]

On 6 Jul 2005 at 21:02, Ron ZL1TW wrote:

> I find the noise of the little fan on the K2 quite annoying, and for some
> time now, I have been using a computer muffin fan which I have mounted on
> a
> plexiglass plate that fits over the heat-sink fins, and is located there
> with a couple of "keys" that fit down into the fins. There is a hole cut
> in

I picked up a couple of hard drive fans at Dayton for about a buck each. They are
already are mounted in pairs and the right size to cover the most"active" half of the
heatsink. Wired in series they run at a nice steady rate and don't cover the speaker at
all. I agree with Ron about sound deflection - makes a big difference as does a resonant
tube over the speaker for "free" filtering!

73,

Peter Linsley, G3PDL

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