The 705A is an EHT power rectifier with a PIV rating of 35,000 Volts. The average rectified current is 100 mA with a peak of 500 mA. The construction is all glass with the lead-out wires being fixed to the main pins that are held in a ceramic disc outside the envelope. The special base clamps to this ceramic disc.
The anode is held in place by the strut connecting to the top cap. Three cooling fins at 120 degrees to one another are stitched together to form the anode.
The central support is connected to the filament centre tap. The image shows the two helical halves of the filament joined to the central support. The construction of the anode is also apparent.
The special ceramic base. The pillar and hook at the top right are the valve retaining mechanism. The annular base is 82 mm outside diameter and 46 mm inside diameter. The insulated legs are 32 mm tall.
The underside of the base. Note the way the sockets are formed so as to grip the pins tightly.
The wide glass tube envelope is 57 mm in diameter, and excluding the B4A base pins is 112 mm tall.
References: Datasheet & 1040. Type 705A was first introduced in 1943.