6SN7 VT-231 5692 Tube Audio Performance – Chimera Labs Revised 05/2003

This is the fifth update on the sound performance of the vintage 6SN7 types. I want to thank all the customers who have sent me their evaluations of these tubes. Let me stress that the optimum tube for your system will depend on your equipment and how your ears judge the tube's ability to reproduce live music.

Customers with Single Ended tube amplifiers and Atma-Sphere OTL amplifiers stated that the difference in performance was easy to hear. I did find it surprising that their final tube preference was very similar.

The general consensus is that the vintage 6SN7GT types, especially the 1940sVT-231s and “C” Military series(basically the same construction) sounded much better than 5692s and later GTA/GTB tubes in most cases. I must add that the 5692 is a very quiet tube with excellent speed, if you have equipment where 6SN7 tubes are microphonic, a 5692 may be the best choice.

I will again caution everyone that various 6SN7 types have different voltage and plate dissipation ratings. The voltage rating refers to voltage across the tube's plate and cathode. To ensure good tube reliability you should probably run a tube at 70% or less of its maximum plate dissipation.

5692 - 275 Volts maximum & maximum 1.75 Watts per section
6SN7GT/WGT -- 300 Volts maximum & maximum 3.5 Watts per section
6SN7GTA/GTB - 450 Volts maximum & maximum 5.0 Watts per section

Using the general audio application of 250 plate volts, a bias of 8 volts results in 9ma of current and a plate dissipation of 2.25 Watts, we find:

5692 - runs 43 % over maximum rating – It isn’t a 10,000 hour tube when you run it this HOT!
6SN7GT - runs 64% of maximum – coasting and liking it
6SN7GTA/GTB - runs 45% of maximum – Hardly turned on, may outlast you.

When in doubt check with the manufacturer of your equipment. If they provide a schematic with component values and voltages, it's easy to use Ohm’s law to calculate the current and dissipation.
There really is no reason for manufacturers not to provide this information.

Here are the rankings. If you have anything to add, email me and I will add it to the list.

VT-231 Tung-Sol, round black plates - Clean, fast, the best in everything, wide bandwidth, great resolution. If you can’t find the Music, it’s not the tube’s fault.

VT-231 RCA, black plates, rich harmonic structure, beautiful timbre and voicing, wide soundstage

6SN7W Sylvania (Mislabeled by me as the 6SN7WGT), black plates – Tied for second and came in first if your system sounds a little laid back, especially some single ended amplifiers – Excellent low level detail resolution, very immediate sounding with a lot of Slam. There are three types of these tubes, two large bottle types, one has a metal ring and one smaller bottle with s smaller plate structure. The smaller one has better low level detail and the larger ones have more slam.

VT-231 Raytheon, black flat plates - like the Tungsol a little sweeter, nice balance of detail and timbre

VT-231 Ken-Rad, flat black plates - Great Bass, drive, sweet midrange, good bandwidth and

VT-231 Sylvania, black plates, wide bandwidth, well balanced, excellent sound stage and air

VT-231 National Union - good drive and great midrange, softer bass and a touch euphonic

6SN7WGT, Tung-Sol. Black Plate, brown base – Sounds similar to the Tung-Sol VT-231, not as clean

6SN7GT, CBS/HYTRON Black Plate, quiet and musical, the best of the non-military tubes

6SN7GT, Ken-Rad, black base, bass a little tubby, but clean with great ambiance and air

6SN7GT, 6SN7WGT, 6SN7GTA, 6SN7WGTA 6SN7GTB 1950s Sylvania Commercial and Military Green Label “Chrome Dome” or “Silver Top”, first top getter on the list, non-fatiguing, smooth, with good detail resolution, bandwidth and speed. Bass can be a bit warm and exaggerated, a good think if your speakers are bass shy. Does not have the midrange ambience and resolution of the VT-231 types. But very good overall.

6SN7GT, 6SN7GTA, 6SN7GTB, RCA Silver Label Black Plate, Bottom Getter. More musical than the Sylvania Chrome Domes, rich harmonic structure with excellent imaging and sweet non fatiguing sound performance. Good imaging and low level detail resolution. Becomes a little too sweet in equipment that uses a lot of 6SN7 types. Nice combination with Sylvania Chrome Domes and the better 6SN7 “driver” tubes.

6SN7GTA, General Electric Black Plate, the great driver tube? Fast, wide bandwidth, smooth sound at the expense of the of low level detail. Along with the Sylvania yellow Label and TUNG-SOL Top getter 6SN7GTB, a great “fourth” tube in Atma-Sphere amps.

6SN7GT, 6SN7GTA, 6SN7GTB, RCA Silver Label Black Plate, Single and Twin Side Getter. What to get when you combine the bandwidth and speed of the Sylvania Chrome Dome and rich harmonic structure of the RCA silver Label Bottom Getter….the RCA Silver Label Side Getters. But the highs are a little recessed and the bass is a little forward. Low level midrange resolution a little obscured. Overall a very nice tube.

6SN7WGTA, Tung-Sol. Black Plate, brown base – Very good bandwidth, bass, detail and soundstage,

5692, CBS-Hytron, fast, good dynamics, lot of air and great timbre

5692, RCA Red Base, very warm sweet sound, great on voices and jazz

6SN7GTB, Sylvania Yellow Label Black Plates, Top Getter Small silver Getter Flash, Clean sound with good harmonic structure, excellent midrange and bass, high frequency a bit recessed and nice soundstage and ambience. Very good driver tube.

6SN7GTB, TUNG-SOL White Label Top Getter. Very Fast, Clean and dynamic. Excellent bandwidth, good harmonic structure. A little too analytical and it sounds better mixed with some of the more musical Very good driver tube and likes to be mixed with RCA bottom getter 6SN7.

6SN7GTB, RCA, Bottom Getter Orange Labels, rich midrange, warm sound, likes being combined with other 6SN7 types, likes the Atma-Spheres

6SN7GTB, G.E, Gray plates, work horse, lacks refinement, a good tube

It’s surprising how many 6SN7 types came out above those expensive 5692s.

One thing became clear based on customer feedback, combining 6SN7 types seems to work better than using all 6SN7s of the same type. With so many preamps and amps using this tube, you can end up with
Six 6SN7s per channel. It appears combining tubes like the VT-231s as voltage amplifiers and 6SN7Ws or 6SNGTA/GTBs as driver tubes you gain the strengths of all. Using one type seems to accentuate the tube’s weaknesses.

Yes there are a lot of 6SN7 types not listed, many of them very good tubes. Based on my own personal experience and customer feedback, the Brimars and Mullards(except for the B65), are good tubes but do not offer the performance of the best US vintage tubes.

The currently produced tubes are about as musically satisfying as a “Boom Box”. I can’t understand why today’s manufacturers don’t just copy some of the great ones. If you are out there, Russia, I will provide free samples. You did it with the 12AX7LPS, do it with the early Tung-Sol, RCA and Sylvanias….Sorry just had to stand on my soapbox for a second.

Best Regards, Dennis Boyle

Vintage Tube Sound Performance and Information