October 1935 Radio-Craft[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Radio-Craft was published from 1929 through 1953. All copyrights are hereby acknowledged. See all articles from Radio-Craft.
While working on vacuum tube based USAF air traffic control radar and radio systems, and having seen many tube television and radio sets I never recall seeing one of these form-fitting metal shields. All the ones I've seen are simple cylinders that slide over the tube and either twist into a receiving rim slot or they have spring metal fingers that grab the glass envelope. As you might guess, utilizing a metal shield around a tube for anything other than a low frequency application like an audio amplifier or poser supply requires circuit design that takes into account the capacitive effects of the large metal plates.
Fitting tightly around the glass, these shields are designed for use with· the new g lass-"metal" tubes, making them interchangeable with the metal tubes in sets designed for the latter. The shield is in four parts, the two main shell pieces being held in place by the top and bottom pieces, which snap into place. The bottom piece has a tab which springs over the ground pin on the tube, and thus grounds the shield as in the metal tubes.
Posted November 3, 2015