| I've spent a lot of hours monkeying with old reel-to-reel decks and making extended tape loops and so forth. The problem with using one as a delay is that the delay time is a combination of the tape speed, the length of the tape loop, and the distance between playback heads. Note "heads", you have to have more than one playback head, separated by some small distance from each other. Either that, or make the tape loop as short as mechanically possible, and speed up the tape until the delay time is likable. So to mod a cheap old reel machine you'd need to do either add one or a few more playback heads, and a mixer circuit to combine all their output, or re-position the pins and rollers around the one stock head in order to make a very short circular loop. A 4-track reel deck will have the mixer circuit built in already, so you could disconnect the wires from three of the playback transducers (there are four mounted into one "head") and attach them to newly-added playbeck heads that are spaced a little bit apart. | 
