5bc3 why such a weird tube

[peverett]

Philco did use some glass Octal type tubes in their radios following WWII. I have some of the "Hippo" models from this era. The tube line up varies from all loctal(The tube type Philco and Sylvania developed to combat the metal octal tubes), to loctal/octal, to loctal/miniature to loctal/octal/miniature.

I suspect this is due to tube availability issues at that time.

I have never seen a Philco radio with an original metal tube though. Philco seems to have used the loctal tubes exclusively in the sections of the radio that a metal tube would have been appropriate for(until miniatures took over).