The 6146 is a very popular small transmitting beam tetrode valve normally used in pairs within HF transmitters of 100 W output. This exhibit is the Zaerix implementation.
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 anode has rounded ends and at the centre of the two working faces are the flanges formed by the stitching together of the the two halves of the anode. Thus at the main heat generating sites are located the extra surface area required to dissipate the heat generated.
Looking at one end of the anode with the two flanges and the stitches holding them together.
The wide glass tube envelope is 38 mm in diameter and excluding the IO base pins, the valve is 82 mm.
References: Data-sheet & 1040. Type 6146 was first introduced in 1952.