The LS6A was the valve that MO-V developed into the PX25, and in this later example the design differs very little from the PX25. This LS6A has two oxide coated filament hairpins and the PX25 has four.
The original LS6A design uses a thoriated tungsten filament that shows the characteristic orange glow when operating. This valve lights with the expected dull red.
The anode is carburised and larger than the original LS6A. The box anode is held rigid by four struts that fix to a collar that is clamped to the pinch. The holding bolts can be seen.
The MO-V etched identification lozenge. In the background can be seen the two oxide coated ribbon filaments and their tension springs. The construction employs a glass rod rather than the later mica supports.
The glass rod support for the filament tension springs. Behind can be seen the substantial copper grid support and the large heat dissipating radiator fin. On the right is the other radiator fin.
The pinch end of the anode. The filament is powered from the outer connections and the centre support has no electrical function. The notched and peened grid supports are easily seen as is grid wire.
The balloon envelope is 60 mm in diameter, and excluding the B4 base pins is 143 mm tall.
References: 1043 Type LS6A was first introduced in 1929.