Set up the two reel-to-reel players next to each other. Set them far enough apart to create some distance between the tape and record heads of each. Clear them of tape and clean the heads using cotton swabs and isopropyl alcohol before performing tape echo with these players to make sure that the fidelity of the sound is high, at least enough to get a good quality of sound and echo.
Place the reel on the post of the right side of the player and pull the tape through the first play spool, which will be located below and slightly to the left of the reel. Start off as if you are feeding the tape through to the play and record heads as normal, but feed the tape past the second reel of the right-side player and continue to the left-side player.
Feel the tape through as you did on the right-side player. This will allow the tape to be read by the play head of the left-side player. Place it in between the pinch roller and the play bar, which contains the play head. Feed it up and through the other side, up and through the record head, which is just below and to the right of the uptake reel. Connect the end of the tape to an empty reel for uptake. Set the reel on the reel table, which is the circle that spins the actual reel, to complete the setup process.
Set up a cable that sends the signal you will be using the echo on back to the original, right side player. Plug the cable into the left-side player's output and into the right-side player's input. This will create the infinite echo you will hear when the players are turned on and the left side is in record mode. This cable will create the path for the signal to be effected by echo.
Plug a microphone or guitar into the left-side player's input. Set the record on the left side player as press play on both of the machines. This will start both of them at the same time and when you play the guitar or sing, you will be able to hear the echo as the left side player send the signal over and the right side then sends it back, thus creating the echo that you hear when you play the instrument or sing into the microphone.