(1) Tested Sylvania Type 27 Tube Date Code 13R Medium Mu Triode Tube

(1) Tested 1937 RCA Radiotron Type 27 Tube Red Letters Medium Mu Triode Tube

(1) Tested Delco Type 27 Tube Date Code A8 Medium Mu Triode 27 Tube

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

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

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

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

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