I think what EdBass is trying to get at is that the EL34 has it's suppressor grid on a separate pin, where the 6550 doesn't. The 6550 (like a 6L6, 6V6, etc) has the suppressor connection internal to the tube to the cathode.
Normally a 6550 amp has to have pin 1 (suppressor) connected to pin 8 (cathode) on the socket for proper pentode operation of an EL34 - not just have the bias reset.