After dabbling with different 6SN7's on my MP-3 I stayed with the CV-181-Z the BT tubes, these to my ears sound better than many of other tubes including NOS.
I tried the Russian Melz (from Romania actually new or with minimal use) not that good, similar to the stock Shuguang
Tried the Sylvania's from the 40's 50's, 6SN7GTB, 6SN7W (bad boys I believe) different pairs, all testing good on my calibrated and restored B&K707, very good but no on par with the BT's, there is a brittle / harsh sound with the high frequencies which is annoying, granted maybe with my Klipsch P37F which lack on the bass this is more apparent than with other systems but I remember even with a sub the vocals had that "shhhhhh" at the end. The BT has a little more bass, black backgrounds etc. So far I have them for 120 days or so with no issues.
I tried the PSVANE's the CV181-TII and the sound was between the Sylvania's and the BT, but one of the tubes died, stop working, when gently shaken it rattle inside and after a week or two the top was all whitey like humidity and condensation got inside. Don't know is this PSVANE was faulty or not, maybe just a coincidence.
For the price for the MP3 I believe the BT is a great tube, you can get a pair on Ebay for $95 / $100 whether a pair of good NOS Sylvania's are roughly the same (from reputable vendors), time will tell how good the BT's are. I am planning to post with no bias (I am actually a fan of american manufacturing and quality especially from those good ole days) but I have to admit that lately the quality of products coming from China has improved and while the prices have also increased that difference is not proportional which makes it attractive.
Oh, on the MA-1 replacing the stock Shuguang for the Sylvania's aforementioned above was a big improvement and this is I believe very specific to Atmasphere, it might not be the same with another amp and another brand. I just had wished the Atmaspheres would have a slightly wider gap between the drivers sockets to accommodate these boutique tubes.
Last but not least the stock chinese tubes are amazingly good in quality and sound, the MA-1 bass will be improved with the NOS Sylvania's but you may lose a little bit on the mids, I'm not actually quite entirely sure about this assertion because the bass improvement may trick you into thinking the mids are not there as before, so basically you are trading sounds based on preference
I believe these amps and pre amps are "chameleons", you can replace the tubes and you have a new amp / preamp at your disposal with different sound and attitude. I'm not going back to SS (at least not on my plans)
I have been wanting to get an MP-1 but the MP-3 sounds so so good that I don't know if I will notice the improvements.
@dragon_vibe can you post your experience with tubes and the MP-1 in general please? I am very curious
Best to you all
Luis
