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August 1935 Radio-Craft
 [Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
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If this Radio-Craft magazine
article is accurate, it was sometime around 1935 that the 8-pin glass-encased vacuum
tube base came into existence. The glass-metal designation refers to these being
glass enclosed equivalents to otherwise metal encased vacuum tubes. Evidently, the
relatively new (and expensive) line of metal tubes sported 8-pin bases so these
glass tube designs had to conform in order to be suitable substitutes.
Just Announced - A New 8-Prong "Glass-Metal" Tube (754)
 Design engineers and Service Men now are
all agog about the latest in electronic devices - a line of tubes having 8-prong
bases, and with identical characteristics to the new 8-prong metal-envelope tubes,
but having a glass envelope. Two of these new "glass-metal" tubes are illustrated;
they are the 6K7 and 6C5, electrical and mechanical counterparts of which (as to
characteristics and bases), except for the envelope, are found in the "metal" series,
under the same designations.
Design engineers are using these glass-metal tubes until such time as it is convenient
to substitute metal tubes as direct replacements. Service Men probably will use
the glass-metal tubes for some time to come as service replacements of metal tubes
(which new sets are being designed to use), until such time as the production of
metal tubes reaches the point where they offer greater competition to the new, relatively
low-price glass-metal tubes.
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