We have seen 10,000 hours and more out of our vacuum tubes without signal degradation. We accomplish this by regulating and filtering the heater voltage to the tubes, greatly increasing their life, something of a rarity if this industry. So, time is not as much of an issue as is sound. If you hear a ringing sound in your audio or when you rap your knuckles on the front, the tube is going microphonic. If you hear an increase in the noise floor, the tube may need to be replaced. Contact us if you need new tubes, we can help.