New-Old-Stock (NOS) tube.

The 6021 is a subminiature medium-mu twin triode for use in general purpose amplifier applications. Each section has an individual cathode and is electrically independent. The 6021 is a special-quality tube for use in critical industrial and military applications in which operational dependability is of primary importance. Features of the tube include a high degree of mechanical strength and a heater-cathode construction capable of withstanding many thousand cycles of intermittent operation. When used in on-off control applications, the tube will maintain its emission capabilities after long periods of operation under cutoff conditions.