I was wondering if there is any way to convert my vox AD120 2x12 combo amp into a speaker cabinet, to use with my Orange head.

Any response is appreciated.

Well if you don't want to do any work, you can simply just unplug the speaker jack at the back and then plug it into your head.

Otherwise, you can just detach the speaker and put it in a pre-made or a DIY cab.

You might want to get a proper cab though, with a better speaker. Avatar Cabs are pretty good for the price.
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