[Elecraft] KPA100 100% Duty Cycle - Operating Temperature

[Don Wilhelm]

Bruce,

If you had the fan turn on at 20 watts, there is likely a problem.
Get an external wattmeter and check the actual power output.
I suspect the actual power is not controlled, and can exceed 150 watts.

The usual cause of that problem is damaged diodes D16 and D17 in the KPA100.

There will usually be no harm to the KPA100 PA transistors, but the PA 
transistors in the base K2 can be damaged because they are being 
stressed to produce their maximum output.

Also that condition is likely to give you a distorted signal, and with 
Data Modes that usually means a high IMD.

73,
Don W3FPR

On 11/4/2017 6:55 PM, K1FFX wrote:
> I started running some 100% duty cycle operation with my KPA100 (PSK31 and
> Olivia).  I was running 20 watts ... I'm not sure what power folks normally
> run in these modes (I'd be happy to get feedback on that), but, in any case,
> I was running well below the KPA100's 100 watt maximum.  After around 90
> seconds, the little fan on the KPA100 kicked in and really rev'ed up.  The
> heat sink was, not surprisingly, quite warm to the touch.
>
> So, considering I was running at 20 watts, would that level of heat be
> normal, i.e., was it actually no surprise that the fan kicked in?  And is
> there any danger to the output transistors running key-down at the 20 watt
> level?