The Tungsram PP35 is an audio output pentode from the 1930s. The heater is rated at 0.2 Amps and thus designed for series heater chains in domestic broadcast receivers.
The coating inside the envelope obscures the inner details but the shape of the anode can be seen. It is oval with two side flanges.
The top mica: the heater can be seen inside the cathode tube and the white cathode coating is visible below the mica sheet. The outer two grids are clear in this image but the fine wire of the control grid is much harder to see.
Here the cathode tube can be seen to be tapered at the top to fit the top mica but expands to a wide oval for the emissive section. The control grid is wound on copper supports with heat radiating strips above the top mica.
The classic envelope is 45 mm in diameter, and excluding the B7 base pins is 106 mm tall.
References: 1040 & 1043. Type PP35 was first introduced in 1935. See also1935 adverts.
