The 354V from Mullard is a detector and general purpose audio valve. The design originally operated with a maximum anode voltage of 200 and was improved in 1930 and again in 1935 with the final design having a 250 Volt maximum anode rating. The mutual conductance also increased over the development cycles from 2.4 to 3.4 mA/V.
This 354V from Mullard has the classic shouldered envelope design and is screened with an external metallising paint. Where the paint has worn off the glass underneath is opaque.
The original 354V triode dates from 1929 and in 1935 the heater current requirement was reduced to 0.65 Amp. This example has a 0.60 Amp heater and thus can be dated to the mid 1930s or later.
The inner coating obscures the details. The control grid heat sing can be seen as can the pinch stem.
Looking up from the base the anode can be seen to be formed from wire mesh.
Top View. The closed cathode cylinder has a reduced diameter than passes into the top mica. The grid winding is hard to see.
The classic envelope is 42 mm in diameter and, excluding the B5 base pins, is 90 mm tall.
References: Data-sheet & 1043 Type 354V was first introduced in 1929. See also1929 adverts.