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In Reply to: RE: Most commonly it is not steel, but... posted by jea48 on June 19, 2016 at 08:38:44
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.
Follow Ups:
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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