[Milsurplus] Audio Output Tranny- Mystery Failure Mode

[David Stinson]

Working on the Navy REP Moral(e) receiver.
It has a single-ended class A 6V6 output.
Audio level is about half what it should be and distorted.
Substitution shows the problem to be both the output 
transformer and the internal speaker.

I pulled the output tranny.  DC resistance checks show what
one would expect for good windings.  Used a DC supply at
90 volts between points and had no detectable leakage 
between input and output windings or to ground.

Ideas as to what the failure mode in this tranny might be?

73 DE Dave AB5S