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The McCullough type 401 indirectly heated triode dates to 1925. McCullough had the Kellogg Switchboard and Supply Company make his valve designs. The first valves of this type were labelled McCullough and the later production adopted the Kellogg name.
The top of the valve has a second pinch through whick the two heater wires pass to the top cap connection. The heater looks to be housed in a ceramic tube inside the oxide coated cathode. The helical wire grid sits in a cylindrical cavity bright anode with side wings clamped and spot welded to the supports. The anode supports are welded to two struts that are held within the top pinch, thus making a rigid structure.
The base end showing the closed cathode tube and the connection to the base pinch.
In this image the cathode can be seen to be a flattened tube with a central seam. The heater insulation is also oval in shape.
The balloon envelope is 40 mm in diameter, and excluding the UX4 base pins is 120 mm tall.
Reference: Internet. Type 401 was first introduced in 1925.


Absolute Maximum Operating Conditions
Updated November 20, 2016.
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