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Yes your hookup is right. It's showing just a little over 2VAC of ripple. That shouldn't be anywhere near enough to cause the huge hum bar effect you're seeing. This pretty well eliminates the negative supply as the source of the problem.
So check for ripple on the positive supply, first on the 'upstream' side of the spkr field* coming out of the rectifier (there'll be a large ripple here) and then on the 'downstream' side (top of C127A). Then at the top of C116B. The ripple should smooth out to just a volt or two and get progressively smoother the further downstream you go, such as at C116A.
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*The speaker field serves double duty as a filter choke, a common practice in old equipment.
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