KT88 and 6550, what max. dissipation?

[Chrome Dinette]

So, in modern production tubes, when biasing for 50-60% of max dissipation, what figure is one supposed to use? I have seen people refer to the maximum as 35, 40 or 42 watts. I always stay on the low side, but I am curious as to what is actually correct.

[RussB]

teach a man to fish...

http://www.weberorders.com/forum1/tubedata.htm

[Chrome Dinette]

I know what the data sheets say, I just wonder if those figures are appropriate for current production tubes.

Also, some data sheets disagree, I have seen 35 and 40 the most, with 42 listed as an absolute max, which I would't use as a reference.