Vacuum Tube - 1R5 / DK91, Heptode
New-Old-Stock (NOS) tube.
Also known by US military identifier VT-171.
The 1R5 is a miniature pentagrid-converter designed for use as a combined mixer and oscillator in superheterodyne circuits. Because of its small size and high operating efficiency, the 1R5 is especially adapted for compact, battery-operated equipment.