The U52 is directly heated full wave rectifier with a rating of 500 Volts on the anodes and a PIV of 1,400 V. The U52 has a maximum reservoir capacitor rating of 16 µF and a minimum series resistance of 180 Ω.
The remains of the Marconi's Wireless Telegraphy paper label
A close-up of the label.
one anode with the filament forming an inverted V.
The filaments in parallel are made of oxide coated tape. The filament on the right has been almost melted through during the welding to the support.
The top mica showing the tensioning springs and the coating on the ribbon.
A closer view.
The classic envelope is 50 mm in diameter, and excluding the IO base pins, is 112 mm tall.
References: Data-sheet, 1040 & 1043. Type U52 was first introduced in 1938. See also1938 adverts.