![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)
File:Vintage RCA Electron Tubes Wall Bottle Rack For Radio Repair Shops (14893631961).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:RCA Radiotron Electron Tube 891R - New England Wireless & Steam Museum - East Greenwich, RI - DSC06725.jpg - Wikimedia Commons File:RCA Radiotron Electron Tube 891R - New England Wireless & Steam Museum - East Greenwich, RI - DSC06725.jpg - Wikimedia Commons](https://upload.wikimedia.org/wikipedia/commons/thumb/3/38/RCA_Radiotron_Electron_Tube_891R_-_New_England_Wireless_%26_Steam_Museum_-_East_Greenwich%2C_RI_-_DSC06725.jpg/1365px-RCA_Radiotron_Electron_Tube_891R_-_New_England_Wireless_%26_Steam_Museum_-_East_Greenwich%2C_RI_-_DSC06725.jpg)