New-Old-Stock (NOS) tube.

The 5750 is a miniature pentagrid converter designed for use as a combined mixer and oscillator in superheterodyne circuits. Analysis of the electrical characteristics of this tube with those of the 6BE6 will indicate that the 5750 is essentially similar.

The 5750 is a special-quality tube intended for use in critical industrial and military applications in which operational dependability is of primary importance.