This exhibit is labelled very feintly as a D4 New Power. The base is typical of products from Radio Micro. Radio Micro became Dario in 1927 and thus this exhibit predates this time. See alsoSpecial also from Radio Micro.
This appears to be a simple way of getting more power from a single valve, just put two electrode systems in parallel.
The valve is in a sorry state. If it had silver gettering it has been lost and if originally a clear bulb, metal has been sputtered onto the inside of the glass. The grey mass towards the bottom of the picture is metal dust and fragments of the grids.
The triode on the right can be seen to have lost both filament and grid.
An even clearer image of the shattered right hand grid. The left triode also has corroded grid wire. The support rods are also corroded where they enter the pinch. It looks as if the vacuum has failed.
The anode support.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 93 mm tall.