The SP2 is a directly heated battery pentode from 1934, designed for broadcast radio reception. The SP refers to it being a straight pentode with a sharp cut-off rather than the VP valves that were variable μ pentodes. The VP2 is an example.
We also have a later SP2 with classic envelope and top hat top cap. This exhibit shows the glue marks from the old style screw top cap.
With some of the metallic paint removed the electrodes become visible. Also the original lettering on the glass becomes clear.
The corrugated anode is divided into two small plates placed either side of the central section. The suppressor grid is the outer cage and within is the screen grid and control grid. All three pass flat across the anode plates.
The corrugated anode and at full size the three grid windings can be seen. All are wound to different pitches.
While not being easy to see the filament is in the form of a M or two inverted V's.
With some enhancement the filament is easier to see.
The balloon envelope is 48 mm in diameter and, excluding the B7 base pins, is 108 mm tall.
References: Data-sheet & 4024. Type SP2 was first introduced in 1934. See also1934 adverts.
