Turn Table Decision

Most likely a ground issue on the 6200. Check the tonearm ground and ensure the phono ground wire is connected to the preamp ground. 

@ bkrpdx
Shure cartridges have a ground tab on the right channel. If the tab is on the cartridge it should be removed. These are the instructions from the Shure website. Give it a shot!


CONNECTIONS (see Figure 1): R~ght "hot" lead (usually red) to "R," rlght ground (usually green) to RG " Left "hot" lead (usually white) to "L," left ground (usually blue) to "LG " If metal head IS causing ground loop hum, remove the ground tab The metallic cartrldge shleld is disconnected from the right channel ground by the removal of the ground tab

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

use the Dual as a paper weight  Poor choice sonically.  Cling clang  You want clean simple devices - tons to choose from for as little as say $300  Look at Rega, Project, even Orbit.  These are all solid bases and dense (plinths) to cut down vibration, ditto on the platter, decent tonearm and cartridge  No gears or moving parts to make noise (remember the needle is actually kind of a microphone) but a separated motor attached with a gentle belt. SImple, clean, attractive, they sound good too. Most popular inexpensive cartridge, often bundled in with an Orotofon 2m Red or other ortofon which tells me the manufacturers are pleased with the sound.  Try Pro ject T1 ($350 new), Orbit Basic ($179)  Want a step or two up?  The gorgeous Pro Ject Debut Carbon  I saw for $450 on amazon.  

@bkrpdx
If you like the Marantz you should keep it . You should replace the stylus on that 40 year old Shure cartridge. LP gear sells a replacement!
https://www.lpgear.com/product/SHSV15IV.html
BTW, since that table is over 40 years old a new belt might be in order!
https://www.lpgear.com/product/MAR6200.html