[Amps] GS-35B efficiency

[Jim Garland]

If builders find that a GS-35B amplifier is significantly less efficient
than, say, a 3-500Z amp, then could someone explain why that is so? I always
thought that the efficiency is a function of the conduction angle (i.e.,
whether the tube biased to class A, B, C, etc.), and whether the tube is
loaded properly with its plate impedance matched to the tank circuit. I also
know that the input network needs to properly matched, and that stray
inductances at the cathode can affect efficiency on the higher bands. But
none of these characteristics pertain to the tube itself. So what's going on
with the GS-35B? 
Jim W8ZR