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How Metal Tubes Are Made
November 1935 Radio-Craft

November 1935 Radio-Craft

November 1935 Radio-Craft Cover - RF Cafe[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.

In the mid 1930s when this Radio-Craft magazine was published, hand-assembled products like metal vacuum tubes were by far the rule rather than the exception for most products be they electronics, furniture, appliances, automobiles, or toys. Many people lament - even curse - the advent of machine automation in production, but the fact is for the vast majority of things the consistency and quality of the finished component is typically much greater. Toiling at the same task, in the same location, day after day, gets unbearable very quickly for someone like me who likes to accomplish a particular job and then move on to something new - even if "new" is defined as the same type of endeavor but with different materials. There are many people, thankfully, who do not mind monotony and prefer its lack of constant challenge to employment that requires constant new challenges.

There are two vintage videos at the bottom of this page that show vacuum tubes being manufactured.

How Metal Tubes Are Made

 - RF Cafe

The finished product. The metal tube, designed by G.E., is being constructed by RCA Radiotron and many of its licensees. A feature of the new tubes is their small dimensions.

 - RF Cafe

Assembling plate and header. Eyelets fasten the plate to its mica supports.

 - RF Cafe

Placing the metal shell over the completed "mount." The mount is the finished internal structure of the tube, with all elements in place. After the shell is put in place the assembly is ready to be welded. Neither base nor cap are added yet, since heat used in exhausting would destroy them.

 - RF Cafe

The final factory test. Here many separate, operation tests are given to each individual tube to insure that it is as near perfect as possible. It is said that the metal tube design effects a big decrease in the number of rejects due to inferior tubes.

 - RF Cafe

Seasoning the finished tubes. Before final inspection, they are operated for a time sufficient to stabilize their characteristics. (RCA Radiotron Photos)

AT&T Archives: A Modern Aladdin's Lamp (1940)

 - RF Cafe

Exhausting the air from the metal tubes. Pumps draw off the air from the tube as it rotates through the gas flames which heat it to drive out gases occluded in the metal.

 - RF Cafe

Welding eyelets to the header. The metal headers are supplied to this machine with eyelets inserted. The water-cooled welding plunger carries a heavy current to the assembly and welds it in one stroke. These eyelets are the ones through which the leads of the finished tube run, the necessary insulation being supplied by beads of a special high-resistance glass. The beads in the base, and those used in tubes having a top-cap lead, constitute the only glass used in the complete structure.

 - RF Cafe

The sealing machine. This close-up shows 8 assemblies in place ready for the sealing operation. The machine is automatically controlled, and applies a current of 75,000 amperes to the weld for 1/30 of a second! Thyratron tube controlled timing assures very accurate results.

 - RF Cafe

Welding exhaust tube to the header. The tube is held in position by a jig as the operator spot-welds them to the header. Welding is again employed in the exhausting process, since when this is completed, the exhaust tube is pinched together in a spot welder so that the pinch is made vacuum tight.

Electrons on Parade (part 1 - RCA) 



Posted January 17, 2023
(updated from original post on 9/7/2015)

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About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024


    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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