ENIAC used common octal-base radio tubes of the day; the decimal accumulators were made of 6SN7 flip-flops, while 6L7s, 6SJ7s, 6SA7s and 6AC7s were used in logic functions.
Numerous 6L6s and 6V6s served as line drivers to drive pulses through cables between rack assemblies.

Several tubes burned out almost every day, leaving ENIAC nonfunctional about half the time.
Special high-reliability tubes were not available until 1948.
Most of these failures, however, occurred during the warm-up and cool-down periods, when the tube heaters and cathodes were under the most thermal stress.
Engineers reduced ENIAC's tube failures to the more acceptable rate of one tube every two days.
According to an interview in 1989 with Eckert, "We had a tube fail about every two days and we could locate the problem within 15 minutes."

In 1954, the longest continuous period of operation without a failure was 116 hours—close to five days.
ENIAC used common octal-base radio tubes of the day; the decimal accumulators were made of 6SN7 flip-flops, while 6L7s, 6SJ7s, 6SA7s and 6AC7s were used in logic functions. Numerous 6L6s and 6V6s served as line drivers to drive pulses through cables between rack assemblies.
Several tubes burned out almost every day, leaving ENIAC nonfunctional about half the time. Special high-reliability tubes were not available until 1948. Most of these failures, however, occurred during the warm-up and cool-down periods, when the tube heaters and cathodes were under the most thermal stress. Engineers reduced ENIAC's tube failures to the more acceptable rate of one tube every two days. According to an interview in 1989 with Eckert, "We had a tube fail about every two days and we could locate the problem within 15 minutes."
In 1954, the longest continuous period of operation without a failure was 116 hours—close to five days.
ENIAC