I will look at modding mine in the future, the cost is not much to replace the main caps and MOSFETs.
I will also look at a Sylvania tube for it, 12AU7.
1) The output is muted when you first turn it on. It will come alive after about 10-15 seconds. As others have said, optimal performance will occur after full warmup (which is probably dependent on your tube). I have not attempted to time when that happens. These preamp tubes do not get hot to the touch (at least, the V2 doesn't), so there really isn't going to be a whole lot of warmup time (no more than a few minutes at best). I do not personally notice any significant difference between turn on performance and performance after a period of time. Both of my V2's behave the same way.
2) In stock form, the heat sinks for the IC's are too hot to touch. I cool mine with a small USB powered fan, which keeps it cool enough to touch. Some people have reported that heat affects the longevity of this device, so I have chosen to cool mine (at the possible risk of not allowing the tube to heat up fully). Again, these tubes do not run hot, so a bit of cooling really should not affect their performance.
The capacitors I am going to put in mine after modding will be too tall for the stock top plate. At this point, I am planning on leaving the top plate off altogether. One idea I have is to replace the standoffs with longer items, and mount my cooling fan facing down over the top of the whole assembly, using the standoffs. Or I may just use a screen with longer standoffs, and leave the cooling fan separate. I guess it depends on how industrious I feel at the time hah.
Personally, I have found that Mullard tubes are the best choice. I don't keep a d-getter Mullard at my work setup, just in case someone knows what it is (on that setup, I use a cheaper o-getter Mullard that I was lucky enough to buy cheaply, because it's a bit low testing).
Just to be complete, I have also tried Telefunkens, Amerex/Mullards, Tung-Sol tubes, and a couple dozen different American vintage tubes. Yes, I know, I've spent waaaaay too much money on 12AU7's LOL Anyhow, for my gear, the Mullards seem to result in the best SQ. As I type this, I'm listening to music on my laptop, driving a Schiit Modi, into a Bravo V2 with a d-getter Mullard, driving my Beyerdynamic DT770 - 250 ohm cans. This has become my favorite setup (much as I hate to sideline my Schiit Magni).
A suggestion: The late 50's Heath-branded Mullards are a very good deal. They use an o-getter, but they can also be purchased for $35 or so on eBay (vs. $99 for a d-getter). I once bought a pair of them for $50, and they are quite nice for the money.
hi everyone, i just order a bravo v2, going to pair it with my akg k240 mkii. just wondering what tube should i change to have better bass? im using laptop and is there anyway i can pair my fiio e10 with bravo v2 as well?