![File:Trio Of 826 Transmitting Triode Vacuum Tubes, RCA (Left) and Ken Rad (Middle & Right), Made In USA (36229884105).jpg - Wikimedia Commons File:Trio Of 826 Transmitting Triode Vacuum Tubes, RCA (Left) and Ken Rad (Middle & Right), Made In USA (36229884105).jpg - Wikimedia Commons](https://upload.wikimedia.org/wikipedia/commons/1/12/Trio_Of_826_Transmitting_Triode_Vacuum_Tubes%2C_RCA_%28Left%29_and_Ken_Rad_%28Middle_%26_Right%29%2C_Made_In_USA_%2836229884105%29.jpg)
File:Trio Of 826 Transmitting Triode Vacuum Tubes, RCA (Left) and Ken Rad (Middle & Right), Made In USA (36229884105).jpg - Wikimedia Commons
![2D21 Thytron Vacuum Tube. Designed to be used in relay and grid-controlled rectifier applications. MFR: RCA, Westinghouse, Sylvania, GE, Tung Sol, National. SKU: 2D21. New old stock. No longer available for export. 2D21 Thytron Vacuum Tube. Designed to be used in relay and grid-controlled rectifier applications. MFR: RCA, Westinghouse, Sylvania, GE, Tung Sol, National. SKU: 2D21. New old stock. No longer available for export.](https://media.rfparts.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/2/d/2d21_rca_1.jpg)
2D21 Thytron Vacuum Tube. Designed to be used in relay and grid-controlled rectifier applications. MFR: RCA, Westinghouse, Sylvania, GE, Tung Sol, National. SKU: 2D21. New old stock. No longer available for export.
![File:Vintage RCA Electron Tubes Wall Bottle Rack For Radio Repair Shops (14893631961).jpg - Wikimedia Commons File:Vintage RCA Electron Tubes Wall Bottle Rack For Radio Repair Shops (14893631961).jpg - Wikimedia Commons](https://upload.wikimedia.org/wikipedia/commons/3/35/Vintage_RCA_Electron_Tubes_Wall_Bottle_Rack_For_Radio_Repair_Shops_%2814893631961%29.jpg)