[Elecraft] K3 Shutdown on 50MHz CW

[Dick Hanson]

Gentlemen....
Since I will be leaving in a few weeks for CY0 with my K3, I am more than a
little interested in this discussion.

Here is what I know thus far.
I have running my K3, in beacon mode; typical CQs followed by call,
repeating every six seconds.
100 watts out into dummy load.

Been running beacon for an hour thus far with no problems.
Other than my 100 watt dummy getting pretty warm:).
73
Dick, K5AND

>No answers, but maybe a related question...
>
>The rig is a K3 with KPA100 and KAT3.
>
>Having just started to use the K3 intensively on 6m, there is a problem 
>with the PA shutting down, especially on CW. After 10-20 seconds of 
>operating, the RF power disappears. Many of the symptoms are 
>intermittent, showing no clear pattern - except that it only happens on 
>50MHz.
>
>Moments before the power dies, there are one or two warning clicks of a 
>relay. There may also be a "HIGH SWR" warning, but not always - 
>sometimes that warning flashes and it's still possible to carry on for 
>10-20 seconds. (The SWR is actually OK - tested at 100W using another 
>rig, and on a dummy load.) The problem is the same on both ANT1 and ANT2 
>outputs of the KAT3, and either with or without the auto-ATU.
>
>The problem cannot be cleared by cycling TX/RX; but it can always be 
>cleared (at least temporarily) by cycling ANT1/ANT2. That brings the 
>power back, making it possible to limp through a short QSO.
>
>However, there *may* be some relationship to the PA temperature. 50MHz 
>is the only band on which the PA temperature indication is being 
>affected by RF - on CW, it bounces upward by anything up to 5degC on 
>every key closure, and I'm wondering if these  transients are triggering 
>a PA shutdown.
>
>There is no problem on any other band. 
>Back on 50MHz, continuous carrier caused the same kind of instant jump 
>in the indicated PA temperature. The TX did eventually shut down, but 
>the transient changes seem to have more effect than the actual PA 
>temperature. 

>It's all a confusing mess of symptoms... and I may not even be on the 
>right track with the PA temperature. However, I feel pretty sure that 
>the problem *is* being caused by internal stray RF.
>

I have experienced the same behavior on 6m, although I didn't do any
extensive
testing.  Thanks the effort you put into your tests.

Tom, N5GE - SWOT 3537 - Grid EM12jq