Speaking of cars, I know I've heard of people who restore old tube-based car radios replacing the "buzzer" (or whatever it's called) that boosts the battery voltage up to the "B" voltage (I think that's right) with something more "modern" (probably a 555 oscillator and some other parts); the metal can for the original part is more than roomy enough for the replacement, and the new stuff is more reliable.
On my '72 Dodge, there's a mechanical device to lower the 12 volt system voltage to 5 volts for the dash instruments. It's a buzzer kind of thingy. Some people replaced it with a modern voltage regulator to get exactly 5 clean volts, and found that the instruments didn't work right.
It turns out that the instruments needed the erratic 5 volts, else they'd "stick".
