3V4 Pentode. A miniature radio tube by Purotron, Switzerland #21003 | M-Ware
File:Vintage RCA Portable Radio, Model B-411, AM Band, 4 Vacuum Tubes, Battery Powered, Made In USA, Circa 1950 - 1951 (32753344002).jpg - Wikimedia Commons
SND Tube Sales Price List 1 00A -- 3V4
3V4 Pentode. A miniature radio tube by Purotron, Switzerland #21003 | M-Ware