Input maybe?
In the older times the input was given, now we see the output figures for P.A.'s
An single 3-500Z(G) will do 1 kW output in an good amp in SSB PEP, 700 watts CW
With 3 tubes and an decent PSU you can triple that, but soome extra losses coupling the tubes will be added.
The 2 tube amps will do up to 2 kW PEP, but driving those tubes to that power will shorten their life
The Eimac i replaced after 23 years still has 75% of the original output, i lower the output to 900 watts PEP in SSB after the tune up lowering the drive, in CW to 500 watts.
Never needed more power, i rather spend my bucks (euro's) on an better antenna system.