Tungsram and Radio Record made a kind of tetrode with penthode characteristics to avoid the Philips patent on the penthode. In most of the tube manuals these tetrodes are drawn and called penthode.
Literatura
Universal Vade-Mecum, Electron Valves and Semiconductor Devices Section 205, p. 404
- - Manufacturers Literature
Taschenbuch zum Röhren-Codex 1948/49
