[Elecraft] PA Temp

[Don Wilhelm]

Hank,

I don't know how hot is safe for the K3 PA devices, but I would believe 
your 42 deg C is OK.

I am going to go out on a limb and make some assumptions - that the PA 
transistors are operating at 65% efficiency, that they are rated for the 
normal commercial operating temperature of 125 deg C and that the 
thermal resistance to the heat sink is 1 deg C per watt.  If those 
assumptions are correct, operating at 100 watts would mean that 54 watts 
is being turned into heat at the junction, and for that power the case 
temperature should not be allowed to rise above 71 deg C.

If anyone has more specific data, please correct me.

73,
Don W3FPR

hank k8dd wrote:
> How hot does your K3/100 PA run?  
> And how hot is safe?
>
> I was sitting in a pileup at 90 watts and watching the PA Temp - it got up to around 41 or 42 C (about 100 F) so I turned the fan up a notch or two and it cooled right back down to around 20 C (70 F).
>
> 73    Hank    K8DD
>   
>