BTW, around 1980, I took my left-over tubes, lined them up on a log, and used them for target practice. I had me a new 22 rifle. The tubes by then were mostly just trash.
Ah, progress!! I also threw away my slide rules about then.
My wee hand-held calculator was much faster and infinitely more accurate.
I remember opening up the TV and taking out any tube that was blackened and looked like it wasn't working; taking that down to the 5 & 10 and sticking it in the machine to tell if it was good or not; buying the replacement and plugging it in.
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