Burn in procedure for NOS necessary?

[MarcelvdG]

Hi!

I would discourage a burn in procedure with heater voltage and no plate voltage for indirectly heated tubes. Many indirectly heated tubes can develop a interface layer when they are operated without plate current unless they are designed for that.

How about tubes that have neither heater nor plate voltage but are stored for decades? Does the chemical reaction that creates the interface layer also occur in them, or is it so slow at room temperature that you would have to store them for centuries?

According to Van der Ziel in his book Noise, the interface layer can increase 1/f noise dramatically and it can be removed by a burn-in with increased cathode temperature and/or substantial plate current.

 

[DF96]

Valves stored unused for decades are usually fine, except for a little gas which the getter usually mops up in the first few hours of operation.