(1) Tested RCA 6S4A Tube and Box Date Code KP Medium Mu Triode Tube

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

(1) Tested RCA 6CX8 Tube with Box Date Code CR Medium Mu Triode Pentode 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 RCA 6J6 Tube with Box RCA Medium Mu Twin Triode Tube (b)

(1) Tested Raytheon 6S4A Tube with Box Japan Code M14 Medium Mu Triode Tube

(1) Tested RCA 6CX8 Tube with Box Date Code DM Medium Mu Triode Pentode Tube