625D_A-P

This tube is of the "Two in One" style made by A-P but designed by their employee, Henry K Huppert. He aplied for a patent on the tube on June 11th, 1924 and was granted patent no 1,597,893 on August 31, 1926. It is used as a detector. The anodes and grids are connected to the normal base positions but the filament is centre tapped with a soldered connection for this at the rim of the base shell. Early versions used the Shaw "Standard Base" and later tubes had porcelan insulation in the base. Most bases were nickel plated but some were unplated brass.

Branding of these tubes is very confusing. On one side of the base are the words: A-P Radio labs; Pat Pending. On the other side 6 volts .25 amps. In some cases the description "Detector" was also printed. In other cases the only way of identifying the tube was by the data sheet which came with the tube, in the box. This showed that the tube was either a detector or amplifier type.