Hi, quick question, is the tip positive and the jacket negative on a guitar lead?

Im making a cab, and need to know which way to wire the jack for the lead from the amp head to the cab.

RG's & Mesa's
On speakers it doesn't actually matter as long as you are consistent but convention says the tip goes to positive so that everything stays in phase if you introduce other speakers.
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What they said, but also: don't use a guitar cable between your head and cab. Use speaker cable.
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