Ok guys

I have a Denon 59L and Pioneer PL-518 and play both with covers on and down. Guess my ears aren't very good because I've never been able to hear the difference with cover up, down, on or off.
I have a small listening room. I guess that could have something to do with it.

Scaf, first of all, if you listen to cassette tapes, you shouldn’t be here. But yes; leave them uncovered.

Dust cover on or down when NOT playing, up or off during playback. This is what I was taught by the "old-timers" when I was young. The dustcover can exaggerate or amplify microphonics. Turn your system on. select the phono input (do not actually play the record). Leave the tonearm cued in the "up" position. put the dustcover on or down. Gently tap on the dustcover and plinth. Repeat the tapping with the dustcover "up" or off. With most tables and cartridges you should hear a significant difference.

I've seen low mass arms so attracted by static from the dustcover that they are lifted right off the record!  Stands to reason that less static can also attract the arm, even if not enough for full lift-off.  So I NEVER play with the cover down.  Of course, I've has a Well Tempered TT/TA since 1987, whose dustcover is not hinged, so is set aside during playback. FWIW, the oil damped spindle and acrylic platter seems to attract dust and static a lot less than any other turntable I had before...including Duals, HK Rabco, Linn, SOTA, Technics, etc.

I always appreciate your enthusiasm for Technics tables and vinyl playback. I keep the transparent hinged dust cover on a KAB mod’d SL1210M5G down and have no problem seeing the record currently playing.

Thanks. It’s hard to imagine a dust cover on my reference technics turntable. Do you see any dust ?? It’s much better without dust cover, i am the one who will never play any vinyl covered by dust cover on any turntables, no matter what , haha

I have my first pair of Technics SL1210mkII since 1995 and believe it or not the dust covers for both are still in the original boxes, i have never used them.

Even with nothing on the platter, leaving the cover in place limits dust reaching the mechanicals of the turntable and should keep the mat cleaner too.

I do clean my turntables and mats from dust. My old pair of Technics still like new and they are open (no dust covers) for 25 years.

I have very nice Dust Cover with my Denon DP-80, but i don’t like how it looks when DC up, and i can’t use it with DC down (not my style). Big dilemma for me.

Both Dust Covers on my pair of Luxman PD-444 were smashed and cracked in transit, so i removed them.

FWIW - in addition to changing the stock feet to threaded spikes resting on a heavy wood platform with layered isolating materials under each corner, I also use small gel "bumpers" on the plinth where the dust cover will rest when lowered. Finally, a weight is placed on the top of the closed cover during playback.

ISONOE replaced stock Technics footers long time ago, my upgraded 1210 are on the custom made metal table filled with sand. Or on the rack when temporary in the main system for the short time.