Vacuum Tube - 3Q4, Pentode, Power
New-Old-Stock (NOS) tube.
Also known by US military identifier VT-264.
The type 3Q4 is a miniature type power-amplifier pentode designed for use in the output stage of battery operated equipment. The filament is center tapped to permit operation with either series connection on 2.6 volts or parallel connections on 1.4 volts.