6SN7GT VT231 TUBES

All of them are pretty great, and the final choice is going to be very system & listener dependent. More often than not, I like Tung-Sol black glass round plate 6SN7 the best - if I had to pick one, that's it. Unfortunately, I've had the bad luck of heaters going out on a few of these. 

I prefer Sylvania (side getter) VT231 over RCA. Sylvanias in general (through the 1950s) are pretty cool with me. Next are Hytrons and Ken-Rads. And RCA last (but still nice). I haven't had the pleasure of trying the Raytheon VT231, but they look lovely! Heck, even the Russian issues (Electro Harmonix, Tung-Sol) can be good - they measure VERY strong in transconductance, and can sometimes be best-in-slot for driving lots of big KT tubes. 

What I found is that vintage 6SN7GT tubes are best suited for the input stages of power amps. In these slots, you're getting all of their sweet sound with none of the downsides. In preamps, these old tubes are going to have all kinds of noise / microphony issues. Even worse in phono stages. As an output stage tube in headphone amps (this was more popular circa 2000s head-fi), they are very weak compared to many other better alternatives. 

For preamp slots, it's best to stick to later GTA / GTB issues (lower noise & microphony), or modern Russia/China tubes which can be selected for very low noise (and matched tightly, to boot). 

6SN7 is a GREAT tube, but it's important to respect its proper role and limitations. 

I have a pair of Sylvania VT 231. 6SN7GT on my OPPO 105 Modwright and when I open the drawer on the player I can hear the noise of the opening on my speakers

Are these normal??

@zorro

That’s very normal for vintage 6SN7GT in "upstream" slots. That’s why I mentioned I hate these tubes in anything but power amps - where they’re far enough downstream from most of your system’s net gain (gain structure). The problem is:

1. 6SN7 has very LARGE plate structure compared to its moderately high mu / gain
2. Vintage 6SN7GT (and VT-231) are very old, and its large mica spacers are not holding the internal parts as tightly as they should, especially after all these years. Later GTA and GTB variants improve the plate & mica structures for this reason; you might try those though they don’t sound as "sweet" as GT.

And yes, any mechanical switches or motors in the SAME box as a 6SN7 is going to cause audible mechanical feedback. That’s not specific to 6SN7 - I have 6H30 preamps with the same issue (they are very sensitive to this). Tube dampers are worthless for this; don't even bother - the problem is how they are mounted to the sockets and PCB / chassis. 

Anyways, if your Oppo 103 has a digital volume control (I forget if it does or not), and you’re using this to directly drive your amps, your problem is gonna be SO MUCH WORSE. If you had an analog preamp with volume control, then that attenuator is at least able to filter some of the microphonic noise (a downstream attenuator reduces the "net gain" the 6SN7 sees downstream). By contrast, the Oppo’s digital volume occus before the 6SN7, so your tube noise effectively bypasses it.

Frankly, 6SN7 here is a rather sadistic choice on part of the modder.