In other words, no - the filament voltage is 5v and a 2A3 wants 2.5v. You could re-wire for 2.5v but then the plate dissipation would quickly ruin the 2A3. Unless it was a 2A3-40, which is a 2.5v version of a 300B, in which case why would you want to go to all that trouble?!?!