the best 2a3

I didn't notice any particular heat issues with the JJ's, but, I was not paying much attention either. Because you mentioned a cover, you should look into whether the JJ's will fit your amp. The tube is taller than a typical 2a3 (the EML's are tall as well).

Does the jj 2A3-40 will produce a lot of heat? since the are 40watts?

will it burn cover of amp?

The JJ2A3-40 is a nice, robust sounding tube, but, for cost is no object, I like EML 2A3s, particularly the meshplate tubes--very large soundstage and extended top end.

In my opinion, the Shuguang 2A3C is a best buy 2A3, and far superior to the Sovtek.

Shunguang 2A3C or sovtek, who's the best?

I've only had the opportunity to try 3 so far; Ken Rad smoked glass, Sovtek, and JJ/Tesla 2A3-40. My preference, and by a large margin, is for the latter. If you want some more info about them, then check out the
6moons review - jj/tesla 2A3-40
.

I too own & love the Shuguang 2A3C. Looks more like a 300B.

suggestion for 2):

Super TNT Shuguang 2A3C - detailed, extended, with a good control in the bass. So far I prefer this one to Sovtek and RCA blackplates.

Not- Sophia ceramic plate

Is- Electro Harmonix