The 30A5 is a power audio output pentode designed for operation with low anode voltages and in transformerless designs. It can deliver 2.1 Watts at 11% total distortion.
Looking through the small notch in the anode the three wire grids can be seen. The inner two being close to the cathode and the suppressor being a very wide pitch helix close to the anode.
Thanks to Graeme Hirst for sending these valves for photographing.
This view shows the copper support rods for the two inner grids the outer grid is not required to dissipate significant heat and does not require the heat conduction of copper. The cathode tube is flattened.
The B7G base with lower electrode connections. In the foreground can be seen the anode tab welded to the anode pin.
The thin glass tube envelope is 17.5 mm in diameter, and excluding the B7G base pins is 60 mm tall.
Reference: Data-sheet. Type 30A5 was first introduced in 1956. See also1956 adverts.
