I just acquired this nice amp and need help. Now this question might sound stupid to most so please humor me. What is the safe plate and grid limit for this amp? so far I drive it with 60w and puts our 650 carrier on the meter. It did a 1kw with 100w drive. I don't mind lower output so long as I don't harm the tubes by exceeding safe limits on the grid and plate. Does not have the low drive upgrade. Thanks in advance.