[Amps] stability of amps

[c.s.]

In my previous "diatribe" I addressed a very annoying issue!! ( IE) 
advertising for amps, that are WAY above the known useful range of the 
tubes being used !!!!
          I have been on this list for a number of years, I've asked any 
number of questions about certain amps, which supposedly are being used 
beyond their useful freq. range, and as of this day I have not received 
any useful answers.!!!! If there are any "REAL" hams here who have"REAL" 
answers, I'd sure like to know.!!!
           Primary to my problems is the question of stability of the 
SB200 on 10 mtrs. 
     there have been a few answers, but certainly not any useful ones.(yet)
 I don't want to step on any toes, but There must be someone out there 
who know's the answers. !!!! If you can make a 572B stable at 50 mhz, 
then why can't it be stabilized at 30 mhz.?????
         carl / kz5ca