Re: SHUGUANG Tubes?
There are only three manufacturers of vacuum tubes, Shuguang in China, JJ (formerly Tesla) in the Slovak Republic, and New Sensor (owned by the same guy that owns Electro Harmonix) in Russia.
Shugs can be found with various labels. They make the Mesa 6L6 STR-440, which is also sold as the Ruby 6L6GC-MSTR. I'm not sure what Shug's designation is for the tube, but I'm sure that they sell it under their own brand as well. The difference is that Ruby and Mesa both further test the tubes before they put them on the market, which I do believe that Mesa is a little more thorough with their testing.
JJs are pretty much just sold under their own name. Their 6L6GC is a damn good tube. Built sturdy and they sound good. I had a set in the Mesa Triple Rec when I first got it (I switched to EL-34s for awhile), and I had no issues with them. And I still have a pair of them, that now reside in my Fender Supersonic 60 head.
As far as the New Sensor offerings go, they sell them under the Electro-Harmonix, Svetlana, Genalex Gold Lion, Mullard, Tung-sol, and Sovtek names. The common misconception is that they are all the same tubes, but they're not. They use different internal parts/designs for each brand. The EL-34S I had in my Recto were Svetlanas. They're good, well made tubes that sound just like the description that The Tube Store gives. I still have them and four of them will probably end up in my Marshall when the stock Winged Cs finally wear out.
And speaking of Winged Cs, they were made by SED (a fourth manufacturer that I didn't list), the original Svetlana (in short, they got screwed out of their name and had to change it). They were excellent tubes that sounded great, but they went out of business in the last couple years or so, and all that's left on the market are used ones and the B-stock stuff. The it's very unfortunate, because they were arguably the best new production tubes available at the time.
Oh, and TAD has tubes from all three current manufacturers, IIRC. TAD is a tester that sorts off the ones that don't meet their standards, and from what I've read, they are one of the more strict testing houses out there. So their tubes are worth their premium if you want the best of what's currently available.