[Elecraft] How hot is too hot

[Don Brown]

Hi

I do this adjustment with a Fluke temperature meter and a K-type thermoco=
uple placed on the mounting screw of Q3. This transistor is the temperatu=
re sensor for the PA transistors/heatsink. I then adjust the CAL temp to =
the same reading as the meter in degrees C. =20

If you don't have a temperature meter you could run the PA a little into =
a dummy load until the heatsink is a little warm then lay a small medical=
 thermometer on the heatsink for 3 or 4 minutes take the reading and conv=
ert to degrees C.

C=3D(F-32)*.5556) =20

You could also turn off the K2/100 and let it settle to room temperature.=
 This may take about 1/2 to 1 hour. Assuming a comfortable room temperatu=
re is 74 degrees F then set the CAL temp to 23 degrees C the first thing =
after turning on the K2/100 this should get reasonably close to the right=
 setting.

Don Brown
KD5NDB

----- Original Message -----
From: kc4kgu@ENTERZONE.NET
Sent: Tuesday, November 05, 2002 11:09 PM
To: K9OZ@aol.com
Cc: elecraft@mailman.qth.net
Subject: Re: [Elecraft] How hot is too hot



On Tue, 5 Nov 2002 K9OZ@aol.com wrote:

> I got the KPA100 running with only minor troubleshooting, and it seems =
to be =20
> running like a champ. Gave it a good workout in SS last weekend. But ca=
n't =20
> find anything on how hot is too hot on the heat sink.
> =20
> If I wait for fan to come on (whether set on normal or low/high) it see=
ms =20
> like the sink gets pretty warm to the touch before the fan kicks in. Th=
e fan =20
> seems to cool it, hold down heat well. So for the contest I just switch=
ed it =20
> to High fan and let it run.
> =20
> But tonight in a casual QSO, top was hot again before fan kicked in. Is=
 this =20
> normal, or should I be checking things twice?
> =20
> Bruce, K9OZ,


Bruce,

When I did the KAT100 field test, the CAL tPA is one of the settings that
I neglected to note.  Since my thermostat is on the main floor of the
house and my shack is in the basement, I didn't have any true reference t=
o
what the temp in the shack really was.

To err on the SAFE side, here's what I did:

I operated the rig into a dummy load until the top cover felt "warm to th=
e
touch" and then adjusted CAL tPA to the point that the fan kicked on.

It's not very scientific but, the fan kicks in when the heatsink gets war=
m
now.

I'm sure someone else will provide a much more scientific method but, tha=
t
has worked for me.

73 de John - KC4KGU
K2/100 #2490


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