The JAN CRP-705A, also known as VT-255 or Raytheon W-3081, is a large half-wave rectifier vacuum tube designed for high-voltage applications. Rated for up to 35 kV at 100 mA, it was used in early radar systems and other military equipment during World War II. In the MicroBasement, this tube represents the rugged, high-power rectifiers of the 1940s — a critical component for converting AC to DC in demanding environments. This write-up covers the tube's history, function, specifications, typical use, and legacy.
The 705A rectifier tube was developed in the early 1940s by Raytheon and other manufacturers (Western Electric, Tung Sol) for military use, released around 1943. The JAN CRP-705A is the Joint Army-Navy (JAN) military designation, VT-255 is the U.S. Government procurement code, and W-3081 is Raytheon's commercial part number. It was produced for radar systems and other high-voltage applications during WWII and the post-war era. Raytheon, a leader in vacuum tubes, manufactured many under contract for the U.S. Navy and Army.
The 705A is a half-wave rectifier that converts high-voltage AC to DC. It uses a mercury-vapor or gas-filled envelope for low voltage drop and high current handling. Key specifications include:
It was prized for its high voltage rating and ability to handle pulsed loads in radar power supplies.
The 705A was primarily used in:
Its rugged design made it reliable for harsh environments, and surplus tubes were popular for DIY radar or high-voltage experiments.
The JAN CRP-705A / VT-255 / Raytheon W-3081 is a collector’s favorite among vintage tube enthusiasts and restorers. Its high-voltage capability and WWII heritage make it a symbol of early radar technology. Today, surviving tubes are rare and valuable ($100–$300 NOS in good condition). In the MicroBasement, it stands as a testament to the era when vacuum tubes powered the first radar systems — a simple rectifier that helped win wars and shape modern electronics.