The Type 38 is an audio output pentode designed for car radio use and operation on a 6.3 Volt DC supply.
The load should be 10,000 Ω and the power obtained is 2.5 Watts. The figures come from Thrower, the Cunningham data-sheet has different operating parameters.
The Tone Master brand is most probably a re-seller.
Circular cathode tube and three wire grids.
Looking up into the blackened anode the circular grids can be seen. Below one can see that one side of the heater is open circuit in this exhibit.
The anode is stitched along the flanges and this clamps the thin sheet to the supports.
The classic envelope is 38 mm in diameter, and excluding the base pins is 97 mm tall.
References: Data-sheet, & 1043. Type 38 was first introduced in 1936. See also1936 adverts.