(1) Tested Very Strong GE 6CU5 with Box Date Code FJ Gray Plate Power Pentode

(1) Tested GE 6CU5 & Box Date Code NF Gray Plate Power Pentode (b)

(1) Tested Sylvania 6CU5 with Box Date Code fh ABY Black Plate Power Pentode

(1) Tested GE 6CU5 & Box Date Code EH Gray Plate General Electric Power Pentode

(1) Tested Very Strong GE 6CU5 & Box Date Code NF Gray Plate Power Pentode (a)

(1) Tested Strong GE 6CU5 with Box Date Code MK Gray Plate Power Pentode Tube

(1) Tested Sylvania 6CU5 with Box Date Code HG EDF Black Plate Power Pentode

(1) Tested RCA 6CU5 with Box Date Code NF Black Plate Beam Power Pentode Tube