BSA, better known later for motor-bikes, issued valves in 1926 under the name BSA Standard. Standard was the brand name of STC at the time who were in turn a subsidiary of the American Western Electric company. The H125 is probably a direct equivalent of the 4215A green spot detector version of the Wecovalve.
This exhibit is fitted with a British B4 base whereas the Wecovalve had a miniature pea-nut base that fitted into a small bayonet base.
The vertical electrode assembly is held in glass beads. Note that the anode is a rolled plate that does not quite close into a full cylinder.
A closer look. The top filament support has a loop to provide some tension.
The bottom of the anode shot with the standard studio set-up.
The same set-up as above but additional spot lighting provided for the shadow inside the anode. This extra light reveals the base of the filament which is intact.
The Etched logo. The font used for the word Standard is the STC brand font. The rear etching says made in Great Britain.
The electrodes with addition of harsh spectral spot lighting.
The top of the anode, again with harsh spot lighting added to the standard studio flash.
Still experimenting with augmenting the flash with continuous sopt lighting of a very high colour temperature (blue white light).
The thin glass tube envelope is 16 mm in diameter, and excluding the B4 base pins is 72 mm tall.
References: 1043. Type H125 was first introduced in 1926.