[Amps] AL80A PROBLEM

[BY THE LAKE]

My AL80A began acting up a few weeks ago...nothing serious but baffling.  On 
160 and 80 mainly, when I tune up with about 30W drive, after a second or 
two key down grid current jumps by about 50 ma, plate current by perhaps 
25ma and power output by about 60 watts or so.  I have done all the usual 
maintenance things and even tried my spare tube but the condition persists. 
It does not seem as noticeable with higher drive and power output.  Watching 
the power output meter on my transceiver, a slight increase is visible 
coinciding with the changes in the amp's meter readings.  Sort of suggests a 
tube about to go bad?  But two of them, one a little-used Amperex??

The onset of this condition coincided with some reports of an echo on my 
signal!

Anybody ever run across this type of thing?

Bill VE3NH