[Amps] Oscillating N6CA 1296 amp

[Dfmich at aol.com]

Has anyone (else) had problems with oscillation in an N6CA "quarter kilowatt" 
1296 power amp?

I have tried different tubes but that doesn't seem to be the problem. 

I am thinking that the loading on the tube may be too light. I cannot find 
anything that speaks to how far the output coupling loop should be inserted into 
the cavity. Anyone have any info on this or the subject in general?

This is an amp that was made by N6CA; ie, not homebrew.

Dan K9EA