The 6146 is a very popular small transmitting beam tetrode valve normally used in pairs within HF transmitters of 100 W output. This exhibit was made by Brimar in England and is new and unused.
The 6146 dates from the era of AM as well as the early days of SSB. For AM a high level modulator was required and a pair of 6146's would provide the audio to modulate the HT for the PA valves.
The Brimar name, BVA and ade in England are printed onto the glass rather than etched. The 6146 is distinctive in the fact that the base is considerably wider than the IO pin ring.
The pressed anode is stitched at the sides and these side flanges connect at the top to the top cap.
Above the top mica is the screen for the grids. In this image the anode straps can be seen to be quite wide and not wires.
The construction uses a glass foot rather than the older pinch. This reduces the lead inductance. Although there is a base cap and outer shell the valve itself is much closer to the all glass construction of B9A valves. In fact the B9D base, introduced after the design of the 6146, would have made this an all glass valve and looked much like the 6BJ6A.
The wide glass tube envelope is 38 mm in diameter and excluding the IO base pins, the valve is 81 mm.
References: Datasheet & 1040. Type 6146 was first introduced in 1952.