"On time" meter for tube life, cartridge life, etc

Does anyone make an "on time" meter. I'm thinking of something that records the number of hours my pre amp stays on, so I can calculate the number of hours in the tubes. I know they're good for thousands of hours, but time passes, and I lose track of time. I wouldn't mind something to use that I could calculate the hours on a cartridge with either. I've a new Shelter 90X, and though I don't get nearly the time I'd like to listen to it, it would be nice to have a timer that I could record the number of hours that it actually contacts vinyl.
How would that help since the time varies on the life of cart and tubes?
The VPI SDS turntable motor controller keeps track of the number of hours during which it supplies current to your turntable motor, which can give you a good measure of the number of hours on your cartridge.
Thanks Cincy Bob. I was actually thinking of upgrading my turntable power supply to the "Turbo" model. I have to look into the price comparison. My Oracle has the speed controls separate form the power supply, so I don't know if the VPI would work or not.

I know the hours vary on tube life, but as time goes by I lose track of time for that much more than I do for turntable use time.