The NT39 (commercially the M-OV ACT6) is a 75 Watt dissipation external anode directly heated triode. The maximum operating frequency for full ratings is 37 MHz.
The old Type designations for Army, Navy and RAF were consolidated in 1941 into common specifications and the CV (Common Valve) register was created. This exhibit has the Post 1941 CV1222 also on the envelope.
The radiating fins fitted over the copper external anode. The ceramic base houses the solid four pins of the T4 base.
The anode connection is of the screw type used in the early 1930's.
Here the shape of the control grid can be seen together with the five supports for the filament. The filament looks to be oxide coated and passes through the grid eight times.
The wide glass tube envelope is 45 mm in diameter, and excluding the base pins is 200 mm tall.
