[Elecraft] [K3] High SWR when running above 12w on 160,80m

[Ilya]

Hi Gentlemen!

Recently I got some strange behaviour in my K3/100 #4413, looking for any
ideas.

When running more than 12 watts on 3.5 and especially 1.8 mhz, the internal
meter shows higher SWR values. The higher the power is set - the higher the
showings are. Like when the power is 20w - it shows smth near 2.0, when the
power is set to 50w - it shows 3.0 and says 'HI SWR'. If I tune antenna
with ATU prior to transmitting - the values are lower, but overall
behaviour is reproduced. Everything looks fine on 40 meters and higher.

But:
1. External meter shows normal SWR like 1.2-1.5 (the real one - the same as
my antenna analyzer shows).
2. If power level is set lower than 11.9 watts - the problem does not
persist (internal meter shows 1 or 2 segments).

Given the description above - I guess something should be wrong in the 100w
amplifier?
Looking for any advice.

Thanks and 73!
Ilya, R3XA