True enough - and we still had some gear that had germanium rectifier stacks in it for odd reasons like that.
Another one that will get you is sneak current through the indicator lamps you added to try and figure out what was going on.
Or an indicator lamp that's also an integral part of the circuit fails, or they try to replace it with an LED on an economy kick, and the machine dies...
That was the failure of the Calling Line Detection systems at the pre-Computers Phone Company - to tell what line was placing the toll call, they sent a 300V pulse down the Control lead and waited for one neon light in the bank of 40,000 hooked to each phone line to fire and pull up a relay that ID's the line. Which worked fine - MOST of the time.
But have a lamp go gassy bad and short (happened every few years) or one time someone tripped and dumped a Big Gulp of Pepsi into the Detection bay, and you're giving out free toll calls till it's fixed.
Now you know how that stupid workplace rule of "No Water, Liquids or Beverages of Any Kind in the Switchroom!" got established.
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