1S5/VT-172

Diode-Pentode Multi-Unit Subminiature Tube, operating with a low-power 1.4V DC filament filament designed for battery-operated portable receivers. It combines a single signal diode with a sharp-cutoff pentode section to act as a centralized AM detector, automatic volume control (AVC) rectifier, and audio pre-amplifier, housed in a standard 7-pin miniature glass envelope (T-5.5 bulb).