[Amps] SB220 transformer capability

[Steve Flood]

Currently I am powering my 3x813 amp with a homebrew power supply built around an SB-220 power transformer.  I have been keeping my plate current to 600 mA based on tube specs, although I've heard I can run the 813s harder than that if desired.

But I am wondering about the capability of the SB-220 transformer.  How much plate current is used in its intended application with two 3-500's?  

Tnx,
Steve KK7UV