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Tech Tip Of The Day: Cathode Danger?

Is cathode stripping a "real" danger to performance, tone, and vacuum tube life?

Provided by Sweetwater.

Q: Someone told me that if I don’t warm up my tube gear before I use it, the vacuum tubes will be destroyed by cathode stripping.

Is that true?

A: Experts disagree whether cathode stripping, which is damage to the cathode surface in a vacuum tube, is is a real phenomenon or not.

Cathode stripping is not a literal “stripping” of the cathode surface, but rather bombardment of the surface with ions, which can physically damage the cathode coating.

In some cases, an electron moving toward the tube’s anode strikes a gas molecule (the vacuum in a tube is never perfect — some gas remains or may slowly leak in), which can cause the release of an electron from the molecule.

With the loss of an electron, the gas molecule now has a positive charge (it becomes an ion), and is attracted to the cathode and strikes it with considerable force. A contributor to this is said to be applying voltage to the tube before the cathode has warmed up.

Many tube experts doubt whether cathode stripping is even possible or ever occurs. Others believe that it can only happen with directly heated tubes. Still others believe that cathode stripping only happens at high voltages (typically above 10 kilovolts).

However, whether cathode stripping is a “real” danger or not, for best performance, best stability, consistent tone, and longest tube life, it is still wise to allow a tube-equipped piece of gear to warm up thoroughly before you begin using it.

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