How Can you use triode as detector in radio wave receivers?

[aliz_khanz]

Homework Statement

How Can you use triode as detector in radio wave receivers?

Homework Equations

N/A

The Attempt at a Solution

when the radio receivers were invented , triode was used to detect them but what function enables this is our of my mind!

 

[Phrak]

Triode/Diode Detector
http://www.vias.org/basicradio/basic_radio_18_02.html"
See the picture. It's just a peak detector for AM transmission.