Once the backbone of yesterday’s “modern” electronics and still widely used in guitar amplifiers today, vacuum tubes are one of the longest lived electronic device families in history.
Troubleshooting these ancient artifacts however has become something of a lost black art.
Several decades ago as a newly minted graduate of a comprehensive military electronics program, I had the opportunity to troubleshoot an old amplifier alongside my grandfather, himself an old WWII radio (Radar) technician.
He stood by silently and watched with great pride as I gathered my materials, Multimeter, Signal source and O-scope, carefully took measurements and poured over the schematics, attempting to locate the culprit.
Claiming it was hard to read the schematics he mostly just observed and listened to me ramble on, bragging about my new-found knowledge.
Then after a while when I appeared to be stuck, the old Pearl Harbor survivor held up his index finger as if to say “just a moment”, licked his finger and quickly touched the top of each tube.
Finding one that was cold within a few seconds, he pointed at it and said “That one is bad.”
And then went into the house to have a sandwich.