Thank you for correcting me and providing more information!

W dniu wtorek, 9 października 2018 17:31:24 UTC+2 użytkownik jrehwin 
napisał:
>
> In the last years of serious tube research and design there was a new type 
> of cathode created, which was as efficient as previous types, but was 
> immune to this effect. Most of tubes designed to be used in digital 
> circuits were designed with long times with no anode current flowing.
>
>
> There are a lot of myths about this, some disparaging metallurgy in the 
> 1950s and 60s, referring to cathode impurities.  They are false.  The tube 
> business, like any business, focussed on volume and cost cutting.  Early 
> on, the tube manufacturers determined that adding a small amount of silicon 
> to the (nickel) cathode sleeve accelerated the activation process, saving 
> time and money.
>
> Later, when computer applications came around, the "sleeping sickness" 
> problem arose, where cathode interface would raise the cathode (and tube) 
> impedance during long periods of cut-off operation.  A little research 
> revealed that this was caused by the added silicon.
>
> The tube manufacturers responded by offering "computer" tubes which were 
> produced without the added silicon, and therefore required the longer (and 
> more expensive) activation.  This worked fine.  To save money, the 
> manufacturers would often use older tooling for the computer tubes, as 
> linearity was not important.
>
> Amusingly, a few modern audiophiles prefer the computer tubes, figuring 
> they must be "better", but in some case, the computer rated tubes will be 
> made with older tooling and have less linearity than the non-computer 
> versions.
>
> - John
>
>

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