You earn amps by
- Making them at the station next to Floyd. Each one will require 10-60 of a collectible item.
- From completing certain story missions.
As I watch a replay of the game, these are the story missions I believe give amps
- 2 Amps from the early tutorial mission on amps.
- 3 Amps for each story mission that involves defending the vats
---- You defend the first vat twice so I think there are 5 of these missions
This should give you 17 amps. Then you just have to use collectibles (sneakers, fizzie, etc.) to buy amps from Floyd. There are plenty of amps that cost 10 so you should easily be able to get enough just by doing the story. If not, Two-Hat sells maps of collectibles. The maps for the first area cost 2500 sodas each, except for the Fizzie Balloon one, which costs only 25 sodas.
Obviously it's completely possible to get the achievement before you're that far in the game. These are just the ones that are straight up given to you.