[G0HZU_JMR]

Looking at his previous posts hillmanie does a lot of work with reel to reel tape recorders. So this might narrow things down a bit. Sadly I have no experience of working inside reel to reel recorders even though I do own an old/classic Elizabethan model. I assume there will be motors inside which might produce voltage transients that could harm a cheapo USB scope if used with a basic x1 probe. There could also be mains voltage and other high voltages inside the recorder.

With this in mind it might be worth buying a scope with a decent voltage rating. Some fairly modern (digital) lab scopes from HP/Agilent or other big brands are only rated to CAT 1 so there is a lot to be said for a traditional (used) analogue/CRT scope from the likes of Hameg/Philips/Iwatsu/Tektronix.

A good solid choice for this type of work would be something like a 20MHz Hameg analogue scope assuming you can find one that isn't very old.