Simple rule is, vintage cabs don't do real lows. Quite often they don't go very high either. If you get a modern cabs that does both suddenly you might find how little low your amp does and how horrible the highs from it sound. Generally the latter more, old amps tend to do more lows than old cabs could reproduce in my experience. If you are keen on the old style heads, a traditional style but modern turbo charged 2x15 with Kappalite 3015s like the Dually or Barefaced Super 15 might be more the thing, those are what I use for very low endy doom.
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