The 154V is a Mullard indirectly heated (4V AC) mains triode that was designed before Mullard's had a satisfactory oxide coating technology and were still largely dependent on the Azide process. Because the azide process broadcast a barium coating everywhere within the anode structure and not just on the cathode surface, it was necessary to design the structure so that all insulating (ie. glass) surfaces and supports were well shielded from flying barium. The classic horizontal arrangement achieved this but made it very difficult to assemble valves with close grid-cathode spacing. Early Mullard indirectly-heated valves therefore had relatively coarse spacings and, as a result, low amplification factors.
The horizontal electrode system. The heater wires can be seen on the left and the grid extends beyond the anode on the right.
Another view of the grid. The glass distorts the image.
One of the welds holding the anode box to the support.
The paper label gives the Type information and operating conditions.
The maximum anode voltage of 150 Volts suggests that this is an early example of the 154V. The first 154V's had a B4 base and side terminal not the B5 base as seen here.
The balloon envelope is 50 mm in diameter and, excluding the B5 base pins, is 86 mm tall.
Reference: 1043. Type 154V was first introduced in 1929.