The MHL4 was used in professional and military applications over many years until it was superseded by the L63, which had comparable characteristics. We have an earlier example MHL4 with a balloon envelope.![](../pics/aaq0350a.jpg)
The Osram paper label.![](../pics/aaq0350b.jpg)
Through the top one can see the three insulated heater loops and the grid supports.![](../pics/aaq0350c.jpg)
looking up from the base the pinch can be seen and above the rectangular lower mica. The anode is a plain grey rectangle.The classic envelope is 44 mm in diameter and, excluding the B5 base pins, is 95 mm tall.References: Data-sheet, 1040 & 1043. Type MHL4 was first introduced in 1929. See also 1929 adverts. |