3 thoughts on “Tung-Sol 6SN7GT Round Black Plates”
The Tung-Sol 6SN7GT Round Black Plates (often identified by their black glass, 1948 production date, and VT-231 markings) certainly carry a massive reputation, but the actual listening experience may not leave everyone “blown away.”
The standout feature of this tube is undoubtedly the bass, which remains unmatched by any other Tung-Sol variant. It provides a warm, open, and fantastic low-end foundation. However, this comes at a significant cost to the high-frequency performance. The top end rolls off very early, making it difficult to hear fine details like cymbals in certain tracks. Consequently, the sense of “air” is diminished compared to what is usually expected from this family.
While this tube could be an excellent tool to calm down an overly bright system, it is difficult to give it a full endorsement for two primary reasons: the “ridiculous” market price and a sonic profile that, while good, doesn’t quite live up to the legendary hype.
Final Verdict: Not Recommended—unless your system specifically requires a heavy treble roll-off and you are willing to pay the extreme premium for its unmatched bass.
Tubemaze– You may wish to give these noble roundplate vacuum tubes a 2nd chance; let them burn-in for a few days to a week, running AT LEAST 8 hours a day, maybe with CD player on repeat, or MP3 player connected to provide input signal. I have found that these old RoundPlate Tung Sol 6SN7s often need some extended usage to “wake up” the cathode and strip off the oxidized layer of barium on the cathode to get down to the strongly emitting layers of cathode emulsion. Before an extended “burn in” or “wake up” period, the roundplate 6SN7s are a little bit sluggish-sounding, and sound a little bit muddled/muddy, and in particular do not have good treble extrension or “air” in the high frequencies. But.. oh, WOW, when these legendary roundplate TungSol 6SN7s DO wake up after some burn in time… they will absolutely blow you away. They combine the midrange layering and dimensionality of the Brimar CV1988 with the sparkle and air on top in the extreme treble response that usually is heard only in the Sylvania 6SN7 W (black base, NOT metal base!!) But it is the midrange that is where the roundplate TungSol 6SN7 makes magic happen. It is difficult to describe; the roundplate 6SN7 by TungSol has such incredible 3-D imaging/soundstaging and such natural, musical timbre in the all-important midrange that it makes it very hard to go back to any other 6SN7 after you have spent a few weeks with the roundplate TungSol. This is my favorite 6SN7 tube… followed by the black base Sylvania 6SN7 W from 1943-1945. After that, there are a lot of 6SN7s that are notable for one or another excellent qualities; the early Sylvanias— Sylvania VT 231, 6SN7W, even the slightly later tall bottle 6SN7 GT– all these typically are the best choice for air and extension in the treble (I call them the Dutch Amperex ECC83 of the 6SN7 world as far as excellence in treble response!) The early gray glass RCAs, especially their VT 231 have excellent balance from top to bottom sonically; they are a very BALANCED sonic signature tube , with excellent, smooth treble and SOLID bass that works well in just about all circuits. I think the black glass Ken Rad 6SN7s are a bit over-rated; they are good but nothing all THAT special. The Ken Rad IS pretty good, please do not think I am saying to avoid Ken Rad… it just is too much money for the merely “good” performance it delivers. The best “families” of 6SN7s are (by far) Sylvania and Tung Sol; even the super common Sylvania 6SN7 GTA “Chrome dome” still has very nice treble and upper midrange and can be had for LOW cost on e*ay. Tung Sol is the other great family of 6SN7s; almost all are worthwhile… and the roundplate is as good for a 6SN7 as the Western Electric 300B is for the 300B family (if that makes sense! Both are “best of breed” types. Love them! BTW– in the right circuit, the RCA red base 5692 is another truly “magical” 6SN7.. but in the wrong circuit or in equipment not optimized for 5692… they can be bloated or “tubby” sounding. But Red Base RCA 5692 is one of the great 6SN7s too!
@ eicoeico Thank you! I have been having similar issues with my Tung Sol RP BG, could not understand it. I ended up doing as suggested and put them on a week of 24/7 burn in. To my delight they improved markedly. I compared 5 different 6SN7 varieties including the Ken Rad and the TS RP BG came out on top with the Ken Rad 2nd from the bottom.
The Tung-Sol 6SN7GT Round Black Plates (often identified by their black glass, 1948 production date, and VT-231 markings) certainly carry a massive reputation, but the actual listening experience may not leave everyone “blown away.”
The standout feature of this tube is undoubtedly the bass, which remains unmatched by any other Tung-Sol variant. It provides a warm, open, and fantastic low-end foundation. However, this comes at a significant cost to the high-frequency performance. The top end rolls off very early, making it difficult to hear fine details like cymbals in certain tracks. Consequently, the sense of “air” is diminished compared to what is usually expected from this family.
While this tube could be an excellent tool to calm down an overly bright system, it is difficult to give it a full endorsement for two primary reasons: the “ridiculous” market price and a sonic profile that, while good, doesn’t quite live up to the legendary hype.
Final Verdict: Not Recommended—unless your system specifically requires a heavy treble roll-off and you are willing to pay the extreme premium for its unmatched bass.
Tubemaze– You may wish to give these noble roundplate vacuum tubes a 2nd chance; let them burn-in for a few days to a week, running AT LEAST 8 hours a day, maybe with CD player on repeat, or MP3 player connected to provide input signal. I have found that these old RoundPlate Tung Sol 6SN7s often need some extended usage to “wake up” the cathode and strip off the oxidized layer of barium on the cathode to get down to the strongly emitting layers of cathode emulsion. Before an extended “burn in” or “wake up” period, the roundplate 6SN7s are a little bit sluggish-sounding, and sound a little bit muddled/muddy, and in particular do not have good treble extrension or “air” in the high frequencies. But.. oh, WOW, when these legendary roundplate TungSol 6SN7s DO wake up after some burn in time… they will absolutely blow you away. They combine the midrange layering and dimensionality of the Brimar CV1988 with the sparkle and air on top in the extreme treble response that usually is heard only in the Sylvania 6SN7 W (black base, NOT metal base!!) But it is the midrange that is where the roundplate TungSol 6SN7 makes magic happen. It is difficult to describe; the roundplate 6SN7 by TungSol has such incredible 3-D imaging/soundstaging and such natural, musical timbre in the all-important midrange that it makes it very hard to go back to any other 6SN7 after you have spent a few weeks with the roundplate TungSol. This is my favorite 6SN7 tube… followed by the black base Sylvania 6SN7 W from 1943-1945. After that, there are a lot of 6SN7s that are notable for one or another excellent qualities; the early Sylvanias— Sylvania VT 231, 6SN7W, even the slightly later tall bottle 6SN7 GT– all these typically are the best choice for air and extension in the treble (I call them the Dutch Amperex ECC83 of the 6SN7 world as far as excellence in treble response!) The early gray glass RCAs, especially their VT 231 have excellent balance from top to bottom sonically; they are a very BALANCED sonic signature tube , with excellent, smooth treble and SOLID bass that works well in just about all circuits. I think the black glass Ken Rad 6SN7s are a bit over-rated; they are good but nothing all THAT special. The Ken Rad IS pretty good, please do not think I am saying to avoid Ken Rad… it just is too much money for the merely “good” performance it delivers. The best “families” of 6SN7s are (by far) Sylvania and Tung Sol; even the super common Sylvania 6SN7 GTA “Chrome dome” still has very nice treble and upper midrange and can be had for LOW cost on e*ay. Tung Sol is the other great family of 6SN7s; almost all are worthwhile… and the roundplate is as good for a 6SN7 as the Western Electric 300B is for the 300B family (if that makes sense! Both are “best of breed” types. Love them! BTW– in the right circuit, the RCA red base 5692 is another truly “magical” 6SN7.. but in the wrong circuit or in equipment not optimized for 5692… they can be bloated or “tubby” sounding. But Red Base RCA 5692 is one of the great 6SN7s too!
@ eicoeico Thank you! I have been having similar issues with my Tung Sol RP BG, could not understand it. I ended up doing as suggested and put them on a week of 24/7 burn in. To my delight they improved markedly. I compared 5 different 6SN7 varieties including the Ken Rad and the TS RP BG came out on top with the Ken Rad 2nd from the bottom.