|
Tubes Asylum Questions about tubes and gear that glows. FAQ |
|
|
|
Tubes Asylum Questions about tubes and gear that glows. FAQ |
|
In Reply to: Re: Cyro treated tubes posted by MIchael Samra on September 24, 2006 at 20:21:43:
I was involved many years ago in a plant that built tubes. The glass was blended with different materials at the tube base pins to better follow the expansion & contraction of the metal pins/wires during heating & cooling cycles. I wonder if the seal could be compromised at extreme cold temperatures on some tubes.The tubes were heated to about 375 degree C, RF was used (like a low frequency microwave oven) to heat the internal elements to cherry red during evacuation. At the end of the vacuum drawdown cycle, the getter material flashed to draw a minimum of 10 to the -6 Torr vacuum. Some high power TV & Radio station transmitter tubes do not have a getter. They required a longer time to pull a vacuum that met specification. Usually an interstage cooler was used in-between the vacuum pump station & the tube itself. I do not understand the mechanics of that, but the cooler somehow attracted remaining molecules out of the tube.
As for thoriated tunsten tubes, the filament contained thorium at a 5% to 10% level. That is a mild form of radiation & is unregulated by the US gov't. The filament was heated to (I believe) 1800 degrees kelvin and a small 'tee shot' of acetylene was added to place a thin coating of carbon on the filament to prevent a high rate of thoria loss. Welding to tungston was performed with molibeium metal.
With all this thorium radiation one would believe the process is a health hazard, but most safety concerns was with the oxide coatings used in cathode type tubes. Years ago, the electronics industry was driven by tubes as solid-state devices were not used in electronic circuits. It was a huge industry that was highly refined.
So, that new manufacture 12AX7 for sale for $7 to $10 each is a bargain from a technical standpoint. I would not want to manufacture tubes today & wholesale them for as low as $3 each in lots of 1000 tubes.
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Re: Cyro treated tubes - Jimmy 04:33:05 09/26/06 (1)
- Make that 2400 degrees Kelvin.............nt - Jimmy 04:36:26 09/26/06 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
