Help With System hum, Please

Maybe the problem is the noise ratio of your preamp, maybe is a bad solderes cable... There are tooany factors here to check

It is hard to tell from your description if the 'hum' is grounding or something
else. I would try replacing the tubes- I don't know much about JJ tubes but
assuming the unit uses standard 12ax7, 6dj8 or other small tubes, those
are easy enough to get from a reliable source. If it is grounding hum, you
might experiment with the following:
what is the relative placement of your phono stage to the turntable?
sometimes, you can get nasties induced through that. Also, any chance the
phono cable is near an AC cable? Laying out the cables to keep low level
signal cables away from power cables is a good idea.
try some other cables as well if you have them. I assume, using a different
source, like CD or radio, no hum, right?
Also, try a cheater plug on the phono stage, just temporarily, to see if it has
something to do with the way the unit is grounded.
Finally, did this problem just exhibit itself or has it been there since you've
had the unit? (if it just started, it could be a tube. I've also had experiences
where I'll get noise through the system through some extraneous source,
like an appliance elswhere in the house, or somebody doing something on
the 'grid').
Marakanetz- I have owned a couple of very good to excellent tube phono
stages and none of them have been noisy. I did have tube noise through
the phono stage of my old SP 10 mk ii ARC preamp, but that would rank as
a 'vintage' unit these days. Modern phono stages should not be noisy.
I also don't think upgrading the power cords will eliminate the problem you
describe, though they may improve the sound, particularly on the phono
stage. I haven't experimented enough with high end power cords on my
motor controller to say whether that will make a significant enough
improvement to justify the cost over the more modest power cord I am
presently using there.

I find that when this happens, not often, if I just unplug all of the cables and wipe the contacts the hum will disappear for a couple of years. Voodoo? I don't know but it works.
Good luck!

;^)

Postscript- I just took a quick online look- the unit has a ground lift switch, and also has adjustable gain for MC cartridges, so some of the issues might be addressed right there- but you may still have a bad tube or more -is the 'hum' in both channels?

I removed my hum after considerable headaches by plugging my turntable motor/power supply into an outlet outside my listening room.