I had Line Magnetic 508 int amp for 2 years which use pair of 6sn7. But recently I got ****t Freya pre to tame the hot sound of Raal Sr1a headphone. Since Freya use quad 6sn7 tubes. I had got good collection of Nos 6sn7 tubes. I received Tungsol Black grass round plate ans Raytheon Vt231 tubes today. I had done shootout between TS BGRP, RCA vt231, KR vt231, Syl vt231, Raytheon vt 231 and Bad boy I played Eva Cassidy's 'Autumn Leaves" "Post card blues " by Cowboy Junkies For classical orchestra, "Trittico" directed by Fennel. "Still harry after all these years" will be for fusion jazz RCA5691, Psavne Acme 300B, Psavne Acme 805 are also being used in Line Magnetic 508 amplifier. Speaker is Lansche 4.1 with plasma tweeter. Digital source is Dave and HMS fed by ripped CD stored in ssd drive of Cocktail audio x30. 1. TS BGRP gave most transparent almost see through sound. But it's tonal balance is slightly skewed to treble, so it could sound hot in bright system. It sound fast but the bass falls way short of the standard set by KR vt231 even behind Rca or Raytheon. Some people are of the opinion that this one is holy grail of 6sn7 tubes doing everything well . But it's bass is disappointing. 2. RCA vt231 is kind of all around player. Compared with TS bgrp, its sound is slightly warmer with lush tone but with enough sparkle and air. It is also very transparent just short of TS. Its bass is also better than TS. I paid only 1/5 price of TS on RCA vt231. But RCA is as almost as good as TS. Thus TS bgrp is over priced due to hype and RCA is a good deal. if you can find Nos RCA vt 231 under 1505, grab it. I had bought 3 pairs of RCA vt 231 with average price of 130$. 3. Kenrad vt231 has best bass among 6sn7 tubes. With KR in it, I got the impression that I do not need subwoofer to get deep bass. It also sound sweet. Thus its tonal balance is kind of neutral. It is pretty transparent just short of TS. 4. Raytheon vt 231. I could grab one RT vt231 at 80$. But it was steal for the performance. Its sound is halfway between RCA and KR. it give better bass than TS and pretty good speed with transparency close to TS. I wish to emphasize again the TS bgrp is overpriced due to hype. I ordered one more RT vt231 at 70$ today. 5. Sylvania vt 231 Its sound is very similar to TS. It has spooky details and transparency very close to TS. But it's bass is too tight but not with enough force. I also have three pairs of Syl vt 231 at average price of 110$ for pair. This one work better in Freya pre in front of headphone amplifiers rather than 2 channel system. 6. Bad boy ( Sylvania GT 3 holes made in 1952 or 1953) This one has good tonal balance (slightly bass heavy) which will work well with bright system. But it falls short of above vt231 tubes in tranparency with limited treble extension. Its bass is full but not at the same level as KR but close to RCA or RT. To conclude, this one is not at the same level as five vt231 tubes in detail and transparency. It is overpriced due to hype. But if your system is on the bright side, bad boy may work. I think it is foolish to pay more than 150$ on it.