(1) Tested RCA 6S4A Tube with Box Date Code K9 Medium Mu Triode Tube

(1) Tested Dumont 6S4A Tube Date Code 61-26 Medium Mu Triode Tube

(1) Tested Very Strong RCA 6GN8 Tube with Box Date Code DL High Mu Triode Tube

(1) Tested RCA 6AZ8 Tube with Box Date Code KG Medium Mu Triode Cutoff Pentode

(1) Tested GE 6S4A Tube Date Code 63-43 General Electric Medium Mu Triode Tube

(1) Tested RCA 6AW8A Tube and Box Date Code BH 6AW8 A High Mu Triode Pentode (a)

(1) Tested RCA 6BQ7A Tube Date Code MZ RCA 6BQ7 A Medium Mu Twin Triode Tube

(1) Tested RCA 6C5 Tube Date Code K3 Medium Mu Triode Black Metal Tube