[Amps] Maximum tolerable SWR for dual 3-500Z amps

[R.Measures]

>
>Is there a rule of thumb for maximum permissible SWR for 3-500Z amps at
>given levels of output power?
>
>Say, 300 watts for 2:1 SWR or 800 watts for 1.5:1 SWR, etc?  For SSB and
>CW modes?

**  If the tank Tune-C and Load-C are not at the stops, the amplifier 
tubes will not know the difference.