You have some electrons over here, and you want them over there but you don't want the electrons from over there to be able to come over here? That's what a diode is for, these are directional current valves and have the benefit of being waaay smaller than vacuum tubes.

Classic 1N4148's are great for any kind of small signal (not power!) rectification. Use them all the time, so they come in a pack of 10. Check the datasheet for more information.

1N4148 Signal Diode - 10 pack (9:44)