Can anyone tell me exactly WHY the AL-80b amp is rated for a maximum 100 watts driving power? Is it because the manual states that, at 100 watts maximum drive, the amp should show a max of 250 milliamps grid current and 600 milliamps plate current which cause the 3-500Z tube to dissipate it's maximum rated 20 watts of power on the grid? These are maximum ratings as I understand it. Anything above these ratings are certain to cause damage. The manual states that USUAL max output occurs with 175 milliamps of grid current and about 475 -500 milliamps of plate current with a carrier such as CW. So, assuming grid and plate current as well as tube power dissipation are most important to watch, is it ok to drive with more than 100 watts if needed to get the amp to produce the rated full output at 175 milliamps grid current? If so, is there an absolute maximum drive level? My amp was bought used. I have no idea how old the tube is. At 20 meters and above, I can get full output with 175 milliamps grid current, or less, at about 80- 100 watts drive. On 40 and 80 meters I have to drive with about 110 watts. On 160 meters I have to drive with about 125 watts. Is this just simply an indication of the tube beginning to show it's age and is getting weaker, and a new tube will allow me to drive with the rated 85 watts or so for full output? Just trying to understand more. It would be most helpful if the manual was more specific and explained things in more detail. But than again, I suppose it's easier to just have the user manual explain the DO's and DON'Ts and the maximum readings, instead of providing more technical information, for most of us.