Vacuum Tube - 3Q5GT, Tetrode, Beam Power
New-Old-Stock (NOS) tube.
Also known by US military identifier VT-221.
The 3Q5GT is a filament type power-amplifier pentode tube designed for use in the output stage of battery operated equipment. The filament of the 3Q5GT is center-tapped to permit operation with either series connection on 2.8 volts or parallel connection on 1.4 volts.