In rectifier circuits, the voltage drop that occurs with an ordinary semiconductor rectifier can be eliminated to give precision rectification. The below shown circuit is the precision full wave ...

This design idea shows an unconventional precision full-wave rectifier circuit with a notable lack of matched resistors.

Helium-filled half-wave rectifier. A 4-pin base with brass shell and ceramic insulator. Tipped S-shaped envelope. Maker's stamping on base reads: "Raytheon / Type B Patented / June 27, 1922 July 7, ...