Underside of K3 getting very hot when transmitting

[Jens Køster]

My K3 100W ser. 1343 gets VERY hot on the underside where the PA transistors
are connected to the chassis. I´m testing at 100W FM into a dummyload for
about 3-5 minutes.

Is that normal?

Vy 73

Jens
OZ9MZ
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[AD6XY]

It is normal - depending on what you mean by "very hot". Very hot to the touch could be 60C. Very hot to a PA device might be 90C or more. It is a good sign your transistors are thermally bonded to the case.

I am not sure you are really supposed to use high duty cycle modes for extended periods like this. The manual mentions reducing power on 100% modes like FM. Using the bottom of the case for cooling generally works OK for low duty cycles but might need help for 100% modes.

My 2m and 4m XV transverters use relatively inefficient PA modules and so also get hot during extended contesting. I found a small waft of air from an appropriately positioned computer fan sufficient to prevent excessive heating. You might try this with the K3. It takes very little air because the surface area is large and you are only dissipating a few watts.

Mike

Jens Køster wrote

My K3 100W ser. 1343 gets VERY hot on the underside where the PA transistors
are connected to the chassis. I´m testing at 100W FM into a dummyload for
about 3-5 minutes.

Is that normal?

Vy 73

Jens
OZ9MZ
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[ac0h]

Jens Køster wrote:
> My K3 100W ser. 1343 gets VERY hot on the underside where the PA transistors
> are connected to the chassis. I´m testing at 100W FM into a dummyload for
> about 3-5 minutes.
>
> Is that normal?
The K3 isn't rated for 100W on FM or any other continuous duty mode,
according to the latest manual.

"*CW and SSB modes,* 100% 10-min. 100W key-down at 25 C ambient"

You must turn the power down on FM and AM or you will burn the finals up.

--
R. Kevin Stover, AC0H

K2/100 #4684
ARRL
SKCC #215
FISTS #11993

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