[old_tv_nut]

This is the kind of sanity check problem we liked to give to potential engineering hires. Not to see if they knew the answer, but to see how they'd approach a sane estimate.

so let's talk orders of magnitude. I'd say the peak tube color TV unit sales were about 10 million per year, and each had about 25 tubes, so thats 250 million tubes per year. If we guess that TV sets were the major use of tubes, lets just use that number as the total produced. Then it would take about 28 years of peak production to equal 7 billion. So, since tube TVs were not produced at peak level for 28 years, the total tubes is less than 7 billion. Throw in some factor for other uses (maybe 2 times), and it would take 14 years of peak production. This is getting to be order-of-magnitude the same as the peak years of tube color TV (maybe 5 years total). So, the estimate of tube production is on the order of 7 billion, but maybe smaller by a factor of 2 to 4 (or 8?).

Feel free to refine this if you want!

Edit: The point is, you can be fairly sure it's neither as low as 700 million nor as high as 70 billion.

Edit #2: I'm going to double the estimate to include tubes for B&W TV made over the years. Still in the same order of magnitude.