New-Old-Stock (NOS) tube.

Also known by US military identifier VT-115A.

The 5881 is the electrical equivalent to types 6L6 and 6L6GC except that the plate and screen dissipation ratings have been increased approximately 20 percent. It embodies a complete mechanical redesign which results in greater resistance to shock and vibration. The use of treated grids and anode greatly increases its overload capabilities and thereby provides desirable improvement in continuity of service. The addition of a low-loss barrier type base will provide obvious advantages in certain applications.