The Cosmos SP-18RR was introduced in the 1926-28 period as an output valve, and part of the Cosmos short path 2 Volt battery valve range. The amplification factor or μ is 6.5.
The Amplion AML2/30 is a rebadged SP-18RR in a tubular envelope.
From the side the thinness of the anode cavity is seen. The grid is a flattened spiral that is fixed to the support rod on one side only. The filament runs through the centre of the grid as normal. In the main picture the anode cavity is on the left with the anode support rod on the right. The diamond getter is also visible as is the coated cathode.
In this enhanced picture the lettering becomes clearer and the Metro Vick logo is visible. Cosmos being a trade mark of the Metropolitan Vickers company.
The balloon envelope is 48 mm in diameter and, excluding the B4 base pins, is 101 mm tall.
Reference: 1043. Type SP-18RR was first introduced in 1927. See also1927 adverts.