[Elecraft] K2/100: PA Oscillation Problem: Help!

[JimWMiller@aol.com]

My newly constructed 100-watt PA has been going into oscillation!
Has anyone else had this problem??  This is a tough one! I've been trouble=20
shooting all day. Please review the following and let me know if you can hel=
p.

1.  Occurs on 20, 15, 12 and 10 meters i.e. higher frequencies.=20
2.  Oscillation causes current surge (blows fuses) and has high amplitude=20
with varying frequency.
3.  This one is interesting! Occurs in SSB when talking/huming loudly for=20
several seconds.  Also sometimes occurs when the ATU is in tune. In other wo=
rds,=20
only modulated signals cause the oscillation to start.  Oddly enough works=20
well in CW (no oscillation) i.e. at least not manifestation of the problem.
4.  NO oscillation in when PA is off i.e. Power < 11 watts. Oscillation=20
occurs when power is between 11 and 100 watts. Seems to occur just as often=20=
at 11=20
watts as at 100 watts.
5.  It's difficult to trouble shoot since oscillation occurs ONLY when PA is=
=20
in cabinet. If removed or =BD removed but still connected by cables, all wor=
ks=20
fine!
6.  Often get "PA HOT" message even though PA is cool. (What's this one=20
about??) =20
7.  Once an "info 80" message was seen.

I'm hoping that someone dealt with a similar problem.=20
Thanks in advance & 73,
Jim WA2UMP K2/100:2679



--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment.  Attachments are not allowed.  To learn how
to post in Plain-Text go to: http://www.expita.com/nomime.html  ---