The J/J 2A3-40 is essentially a 300B, with a 2.5V, 2.5A filament. 2A3 is normally rated at 15Watts PD.
In a Paramour (or Stereomour), it would behave as a 2A3 would, dissipating 15W or less.
Power output would be the same as a "normal" 2A3.
HTH
/ed B in NC