A-P Labs 2 in 1
DC Det/Amp Triode
1923

This tube had an unusual structure with 2 triode sections using a common plate. The 2 grids were connected together and the filament was center-tapped with the mid-point connected to the shell. This arrangement made it possible to run one section at a time but it was not normally used in this way. With both sections in operation the tube was similar to an '01A.