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SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
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SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
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In Reply to: RE: How often do you roll? posted by sony6060 on January 8, 2022 at 06:43:10:
Some tubes DO need broken in.
The issue is called "forming the cathode." It's the final step in making a tube - the cathode is heated, usually a bit hotter than nominal operating temperature, and some DC voltage is applied between plate and cathode. This causes the low-work-function atoms (barium and/or strontium in oxide-coated cathodes, thorium in thoriated-tungsten cathodes) to migrate to the surface, increasing the emission. Nominally this takes place in the factory, but it takes time which makes it costly, so it is often not quite complete. And old-stock tubes that have sat around for decades often need to be re-formed.
A couple decades ago, I measured this in some early production Sovtek 300B tubes, and have since found that bias often drifts for the first 10-100 hours with many tubes. Once fully formed, the bias is very stable.
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Follow Ups
- RE: How often do you roll? - Paul Joppa 07:29:42 01/08/22 (1)
- RE: How often do you roll? - sony6060 07:32:13 01/08/22 (0)
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