I bought some reel-to-reel tape from Thomann, to splice a loop ordinary tape worked fine (of course, proper splicing tape would be better, but costs like a 2nd hand reel to reel ;)).
I found some reel-to-reels on fleamarkets/Ebay/2:nd hand record stores:
capacitors needed changing…
… especially on the cheap ones, but then they normally worked OK. Other notes so far:
• The earliest cheap ones didn’t use a capstan+pressure roller, they just press a spinning motor to a large rubber wheel under the reel.
Reel-to-reels without a capstan-pressure-roller are impossible to use for loops, even if they’re charming. You can almost see the little axis pressing to the take-up reel between the reels.
• The slightly more advanced portable ones use a capstan and pressure roller, these can be used for loops.
Portable reel-to-reels could be modified to include a crude speed control (just regulating the voltage/power to the motor). I haven’t tried this yet.
• The stationary ones often worked with mains powered AC-motor and are trickier to change speed on, they roll very stable, but changing the speed gradually is trickier.
Some stationary ones (e.g. REVOX A77) can be fitted with a varispeed.
But, simpler and cheaper; you can change the distance to the recording head:
Here I put a loop on the mechanically-broken-beyond-repair AKAI I got cheap and mounted this extra head-in-can (from a junked cassette player). Works OK for long delays. One of the first things I built.
Here’s a video demo.