It took me a while to find it... but here it is, a motor generator that can give a gain of 10,000 or more using a bit of recursion https://en.wikipedia.org/wik

It took me a while to find it... but here it is, a motor generator that can give a gain of 10,000 or more using a bit of recursion https://en.wikipedia.org/wiki/Amplidyne https://en.wikipedia.org/wiki/Amplidyne ----- An earlier circuit that gets gain out of Motor Generators is the Ward-Leonard control https://en.wikipedia.org/wiki/Ward_Leonard_control https://en.wikipedia.org/wiki/Ward_Leonard_control At the US Steel works in Gary, Indiana, they have a 6 stand cold rolling mill. This uses pairs of 19,000 Horsepower motors on each stand to pull a cold slab of steel 6 inches thick like taffy to reduce its thickness. The electronics of the day (early 1960s) couldn't drive things directly, but they did have SCR packs big enough to drive the fields of DC generators in the Ward-Leonard configuration. I rebuilt many of those SCR packs in the 1980s.