"The basic, domestic quality thermionic tubes have codes for a projected life span of either 1500 (6Н3П-Е) or only 500 hours (6Н3П). Many were used and then stored for over 50 years, quality stamps may have been accidentally altered, so life expectancy may be questionable, both for the tubes and for me!"

I love the idea of an expiration date, or at least an ever-present need for repair. It emphasizes the idea that the computer is a machine, subject to the constraints of the physical world. There's something charming about that.