[Amps] Real power from GU74b?

[R.Measures]

>According to one catelogue, a GU74b valve will give 600w output, yet I have
>seen one manufacturer of amateur amps claiming he got a healthy 1kw out a
>single valve.
>
>Am I skeptical believing this is a re-run of "we can get 400w out of a
>4CX250b" story, or is the catelogue I have seen the 600w figure quited from
>wrong, as I did see another catelogue quote 800w.
>
>Of course it is always possible to more than a catelogue says one can get
>out of a valve, at the cost of shotening its life...
>
**  Richard --  Much depends on mode.  400w output in RTTY service is 
different than 400w-PEP out in SSB.