[JulioCat]

I have a DAC with a 12AT7 tube from electro-harmonix, how long does it will last? it's better to live it on?

 

[xaval]

Lasting life a tube is pretty uncertain... I have never had a 12AT7 die of old age in my hands, so this means that it'll last quite a few years. As with any electrical appliance, you should turn it off when not working for longer than a day imo. Personally I never leave any of my gear on longer than needed.