[TenTec] Ten-Tec 229B tuner problem

[Douglas]

I recently got an older high power Ten-Tec tuner Model
229B. It's basically the same as the current
production L-network 2KW tuner.

While using 300 ohm line and it's internal balun, the
SWR increases rapidly with key down time when I'm
using 500 watts or more power. The impedance will seem
to shift up, if the tuner is retuned it seems to
rapidly shift down.

The problem is in the tuner since things work fine
with my old Murch UT-2000B under identical conditions.

I suspect that something is heating up.
I've tightened grounding connections and checked the
balun coil for heating (it never seems warm to the
touch). Also, I've cleaned and checked the rotary
inductor connections - seems fine. The fixed
capacitors also don't seem to be overly heating.

Another thing that might be suspect is the phenolic
plastic standoff insulators for the 300 ohm
connections on the rear panel. One arched internally
and I double insulated the connection screw as it went
thru the panel with a layer of 3000 volt rated
shrinkable tubing. No more arcing but the variable SWR
problem continues. I've never seen non-ceramic
insulators used in such applications.

Has anyone seen similar problems with this series
tuner under high power conditions?

tnx,

Doug/WA1TUT