Audio output beam tetrode with octal base

A Pentode is an electronic valve with five electrodes. It is widely referred to as a three-grid amplifying valve. The additional grid is called the suppressor grid, and its role is to give a greater output signal; this is achieved from the plate of the Pentode  when it is in operation;

Power pentodes are designed to operate at higher currents, higher temperatures and higher voltages than ordinary pentodes. A Pentodes has octal base. The most common power pentode are KT61 KT66 EL33 EL34 EL35 EL37 EL38 EL84 KT77 6L6G 350B 6V6G

KT61 KT63 KT66 KT77 KT88 EF36 EF37 EF86 etc