[Amps] EIMAC vs Amperex 3-500

[john.keating at outlook.com]

Spec sheets for these tubes appear identical. Yet they behave 
differently in my dual 3-500 amp. I can drive the Amperex at 90w for 
near-legal limit out (power gain of about 16x) without exceeding 200mA 
grid current; Plate current is just about 800mA for the pair. With the 
Eimacs, I can't exceed 75W drive without exceeding 200mA grid current 
(running about 720mA plate), and they do give the same 16x power 
amplification at that drive. At 90W drive, the Eimacs exceed the 
recommended grid current limit. Wondering if the amp brain trust can 
enlighten me on the difference and cause.

73, John / AI6LY