Automatic tube timer?

I am looking for a simple way to keep track of the hours on my tube amp. This could help to determine when tubes might need replacement, or how long a component has been burning in. The timer should be ultra quiet, and it should measure hours up to 9999, no tenths needed. It needs to come on and off automatically.

One way would be to hook a simple LCD hour meter to the 12 volt trigger on the back of the amp. I know that some amps come with such a meter built into the chassis. It would have to draw less than 50 ma. Does anyone know of a source for such a meter? I have been unsuccessful finding one.

Any other ideas? What have you all tried? Is there a better solution?

Thanks for your ideas and assistance...