New-Old-Stock (NOS) tube.

The 6678 is a miniature tube containing a medium-mu triode and a sharp-cutoff pentode. It is especially suited for use as a combined oscillator and mixer at very high frequencies. The electrical characteristics are essentially equivalent to those of the 6U8. Intended specifically for use in mobile communications equipment, the 6678 may be operated without serious degradation under normal variations in supply voltage as encountered with automotive electrical systems. Also consistent with the requirements of this equipment, the tube is capable of withstanding appreciable on-off cycling.