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Type VT-228 is a VHF/UHF transmitting triode and dates from the early 1940s and has a thoriated tungsten filament as did the earlier 1628.

The control grid can pass up to 14 mA grid current and dissipate 1.6 W. The maximum frequency of operation is in the region of 500 MHz.

The Commercial 8012 designation appears on the glass as well as the US Government code of VT-228.

The lead inductance is keep small by the connections being made directly through the side walls of the envelope.

The close wound helical control grid.

Using the microscope and a great deal of patience this image of the control grid and helical filament was possible.

The thin glass tube envelope is 25 mm in diameter and, excluding the base wires, is 93 mm tall.

References: Data-sheet & ³⁰⁰². Type VT-228 was first introduced in 1945. See also 1945 adverts.

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.