Most stereo hifi speakers are 8 ohm. You could safely run a Vox head into one 8 ohm hifi speaker at low volumes. Set the head to 8 ohms. You can verify your speaker ohms. Just put an ohm meter on each lead and it should read about 6-8 ohms.
There is a way to run two 8 ohm stereo speakers with special wiring at 16 ohms, if you are interested in making the special cable.
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