IMPROVEMENTS TO THE PM SERIES 1926 to 1928 -

Posted by STEVE MYCIUNKA on

The unreliable 'split-pin' PM series were swiftly replaced by valves having a new improved base. The base was characterized by having the same ebonite base but the inset pins were now tubular, having two slots in orthogonal configuration with electrode lead arrangements..outs being passed up the pin centre and connected by soldering at the tips.

The bases now had a paint filled groove also labeled ‘A’ to denote the anode connection adjacent to the anode pin – This paint was applied by deft fingered young ladies but the process was deemed too labour intensive and so was discontinued in 1928, however, the base mould was unchanged so the unpainted groove and letter still remained. Reliabilty was mightily improved by the new connection arrangements.


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