Hi. Lou: "Does the 4CX or 3CX indicate the type and the following digits the size?" ========== "4CX" are tetrodes and "3CX" are triodes (the "CX" indicates Ceramic & eXternal anode). The digits that follow are the rated plate dissipation in watts. You can e-mail Svetlana to get data sheets on their tubes. They probably have a Web site where you can download that data. 73, de Earl, K6SE