The LS6A was the valve that MO-V developed into the PX25, and in this later example of the LS6A the design differs very little from the PX25. This LS6A has two oxide coated ribbon filament hairpins and the PX25 has four coated wire filaments.
The original LS6A design uses a thoriated tungsten filament that shows the characteristic orange glow when operating.
The anode is supported by four stout vertical supports that are brought down to a collar that clamps to the pinch stem. This is not a cheap method of assembly and usually is only seen in professional valves.
The Type designation is etched into the top of the glass envelope.
The twin filament tension spring couple to oxide coated ribbon filaments. The control grid is shaped and passes flat across the face of the anode. The top components are secured into a glass rod. This method of assembly was essential with the messy Azide process but gave way to the use of mica sheets when better cathode forming technologies were developed.
The balloon envelope is 60 mm in diameter, and excluding the B4 base pins is 134 mm tall.
References: 1043 Type LS6A was first introduced in 1929.