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Like a 6DJ8/6922 tube.
Vintage as well as current production. I am talking about the bare metal.
I was under the impression the pins were made of steel.
I searched the net and came up empty. I am looking for a credible Web Link.
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...a special alloy with the temperature expansion coefficient close to that of glass. There are many such alloys, since there are different glass compositions as well.
Thanks Victor for the reply.
Were the same special alloys used for the pins on miniature tubes by manufactures back in the 1950s, 1960s, and 1970s?
I guess the reason I am asking is why so many people, including tube vendors, call them steel pins?
Thanks,
Jim
The term "steel" doesn't always get used in the strictest metallurgical sense. I think steel is commonly used to describe the pins because they're usually quite magnetic. The material I've seen referenced in tube manuals and such is "kovar", a nickel/cobalt/iron alloy with coef of thermal expansion similar to borosilicate glass. The alloy also bonds well to glass and is apparently magnetic too. Seems if one believes magnetic conductors distort music signals, tubes should not be in the signal path...LOL.
Strangely, it is exactly the same name used in Russia.
:-)
I always thought it was a Russian word... silly me. :)
When I was still a little boy, they started taking us to Svetlana factory (I lived two blocks away), where we watched the glass blowers do their thing. It was fascinating. At that time the glass tube was pulled by hand and by feel, two guys stretching the glass bead over a long wooden bed, checking its diameter at some points.
It is interesting, how the leads are done for big tubes. First the guy takes the lead wire and wraps a small area with a glass - as you would with a piece of rope. This way it attaches better to the metal.
The leads then get assembled into the base, their glass-coated areas now melting and fusing into the disc. We made some of those devices literally by hand at our university department... very fancy devices for research.
"First the guy takes the lead wire and wraps a small area with a glass - as you would with a piece of rope."
That explains why the pins of larger tubes often protrude through a glass "doughnut." Also very interesting, the Kovar discussion. I've often wondered why thermal cycling doesn't break the seal over time.
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