[Elecraft] XV432 Oscillates with Amp connected

[Stu2]

Good day,

I'm working with the XV432, Flex 1500 and Henry  2004A Amp. The rig, 
xvrtr and amp PTTs are sequenced. Hoping somebody might have been down 
this path before and has a solution.

If I connect the transverter output to the amp (or different pieces of 
open coax) and key the transverter, the power meter goes full scale and 
I see an oscillation on the spectrum analyzer. The frequency of the 
oscillation varies with the load. (i.e. amp connected or different 
lengths of coax) If I connect the XV432 to a 50 ohm load, no 
oscillations and all works well.

I ran through the alignment procedure again with the XV432 connected to 
a 50 Ohm load. All the voltages look right and the tuning is smooth. 
(e.g. 20mV Quiescent Current Adjustment, TP3/TP4) It's obvious the XV432 
is happy into 50 Ohms, but not into impedances that wander from 50 Ohms.

BTW, I have added all the mods as per the Elecraft website.

Any ideas?

73's
Stu2
W7IY