Turn Table Decision

Upgrade asap.

If the above procedures did not work

Here’s a quick debug procedure that might help...
- get a length of wire - about 6 ft
- attach one end to the ground pin only on a mains plug
- strip about 1/8" of insulation from the other end
- you now have a grounding lead

Insert the plug into any outlet
- touch the other end at various points on the arm to test it for grounding
- start at the head and work towards the back

If the hum goes away then the arm( or maybe the TT) needs to be grounded properly

If the hum does not go away - everything is grounded as it should be and the problem is probably inside the Turntable OR at the cartridge

You could also try - touching the open end of the ground lead to the neutral side of the RCA jack on the cable where the TT wire plugs into the pre-amp

If the hum goes away you can permanently  fix the issue by connecting the open end of the grounding lead to the neutral side of an RCA plug and connect it to any unused RCA jack on the pre-amp.

Whilst this is not the perfect solution it will not harm any components

But I also concur with @ebm - your system components "deserve" a better turntable - technology has come a long way since either of the two turntables you mention,

Regards - Steve

Thank you for the replies. @yogiboy , I removed the ground tab, and the hum is gone. It befuddles me that a cartridge this old would still have the ground tab, when, at least on the Shure support site, this is a known issue.

@ebm @williewonka any suggestions for a replacement TT? Under $1,000, cartridge inclusive? I assume the consensus would be to use the Marantz over the Dual.

I've only had a couple of turntables and am still kind of new to it, but the Pioneer PLX-1000 at $699 could fit the bill. Still leaves you with a few hundred for a cart. Hopefully others whom are much more knowledgeable in this area will chime in. 

@bkrpdx - I like the look of the Music Hall 3.3 (in your budget) and the 5.3 (just over your budget)

Regards