Tight tolerances: In these tubes the tolerance of electrical ratings are reduced in comparision with standard tubes.
Vibration and shock proof: The tube withstands accelerationns of 2,5 g at 50Hz for lenghty periods and momentary shocks of 500g for short periods.
Cathode free from Interface: The cathode establishes no interface even in case where the heated tube is operated without plate current over lenghty periods.
Heather voltage: The average heather voltage should be 6,3 V.
Variations of the heather voltage exceeding the range of 6,0 V to 6,6 V will shorten the tube life. The tolerance of heather current (column II) should be taken into account.
Substitutes: E88CC, 6DJ8, 6922