I've got pretty good double tracking from a crummy cassete recorder
You just record your takes on the cassette recorder and then play them back from the casette deck into your pc (original track) .then rewind and record another pass of it onto another track on your pc(doubled track).
Hopefully they will line up enough that you can make a few snips here and there to one or the other and prevent them from going too out of sync.

sounds less cyclic than lfo's to me and also sometimes the tracks catch up and pass each other for weird "merge phase" anomalies
I think i've read about the beatles also synching recording consoles by the ac frequency feeding power to the consoles..

"George, turn up all the knobs... "