Shuguang
Treasure Series 6SL7 Octal double-triode
![[Shuguang Treasure 6SL7 in box]](../jpg/treasure-6sl7_box.jpg)
[Italian version here]
[ Home | Staff & Contacts | HiFi Playground | Listening tests | DIY & Tweakings | Music & Books ]
Manufacturer: Shuguang
Product: Treasures 6SL7 double small-signal triode
Supplier: Grant Fidelity
Price: $219 tested matched pair, YMMV due to currency volatility
Valve base type: Octal
Reviewer: Mark Wheeler - TNT UK
Reviewed: October-November 2015
"How can electrically similar valves sound different?" challenge plebs, stage left, "This sounds like snake oil, smoke and mirrors, to us".
Nominally electrically similar valves can feature different internal designs, different materials and different manufacturing accuracy. Furthermore, the manufacturer may pitch their specification to one or other ends of the allowable range for any particular parameter. Therefore how each valve will work will often also depend as much on the circuit design around it as any other factor. Design and materials choices affect microphony too, the tendency of the device to turn external vibration into an unwanted signal (unwanted unless the device in question happens to be a microphone). This will have different effects in different environments. Guitar amp builders (historically including Gibson and Ampeg) also know that the 6SL7 has "Octal tone" compared with the electrically similar 5751 miniature. The 6SL7 is a great small-signal valve, useful in situations where the designer does not wish to miss a single electron on the grid. Hence the 6SL7 is a popular choice in the first amplification stages of high-end phono-preamplifiers. However, the bigger electrodes of octal valves often make them more prone to microphony, making vibration isolation a high priority.
The Shuguang design features black glass, described as a "High Polymer Compound Carbon (HPCC) coating" apparently being used for the first time in valve (vacuum tube) technology. This HPCC coating increases secondary electron emission suppression from the glass envelope, compared with the black glass of NOS examples, like your old Scribe's favoured black Brimar octals, whose colour comes from sprayed carbon, which in its turn is arguably superior to clear glass. Getter design is likely to have much influence on this parameter too. This will also affect self-generated noise in the valve, either in character or magnitude, which Shuguang also claim to address with improved vacuuming technology during production. Less internal pollution in valves equals lower noise and longer service life.
Another Shuguang argument to justify their premium price is production process. Shuguang claim that key tasks in the Treasure Series valve assembly are manually completed by a select group of senior staff with over 30 years of experience. There are 60 quality controlled and matched parts in each Treasure Series valve compared to their lesser ranges. Factory testing is then backed up by further testing and matching on arrival at Grant Fidelity's premises, ensuring the journey has not affected the product at that point. These valves have been silk-screen printed "Treasure" at the factory, with the legend "GF Select" added to identify the extra quality control screening. The legendary NOS ruggedised milspec valves may owe much of their reputation, not to their innate superior sound ex-factory, but to their better survival intact after years being heaved about about dusty warehouses.
The valves arrive safely packed in foam. In the box an individual test note has the maker as "Shu Guang". Shuguang means daybreak in English. Grant Fidelity have strong links to their Chinese suppliers, visiting them annually. Grant Fidelity were founded by husband and wife team Ian and Rachel and ran by them until Ian's untimely death last year. Rachel managed to keep the business running while nursing Ian, and Grant Fidelity continues to flourish in his memory. These valves are the same size as the Shuguang Treasure 6SN7/CV181 standing 150mm from the valve socket and 75mm in diameter.
The shouldered glass envelope of this example means it cannot be called a tube, they are not tubular, even if the Valley Girls might think them so, for sure. Reviewing electronic valves is a perilous business. Every time they are inserted or removed from a socket there is a danger that the socket soldering or valve base will be damaged. They need to cool down before being moved and then they must have long enough warming up again to be on song. The time lag between hearing each sample undermines our feeble aural memory. One approach is to use an intermediate high quality source of the same recording to hold a position from which to evaluate differences. Given that the Shu Guang Treasure 6SL7 is being tested in the Canor TP306 VR+ phono-stage the alternative source would have to be an alternative medium or involve unplugging and replugging a different phono-stage while the Canor is undergoing cooling and warm-up cycles. This was tried, using the Chevron modified Shanling CDT100 and various copies of Pink Floyd's Dark Side of the Moon (the only recording owned in several formats by your old scribe) but this was less informative than extended listening sessions.
"What was it that the Old Scribe's sister said about DSOTM?" query plebs, stage left
When asked to contribute to a book celebrating the 25th anniversary of DSOTM, the Old Scribe's sister (another scribe of lesser age) stated that she hates DSOTM with a venom difficult to imagine, having heard it played relentlessly at remorseless volumes by the Old Scribe throughout her childhood. During this review something similar happened, among the other musical gems listed below.
The Canor TP306 VR+ phono-stage features two 6SL7 valves in each channel. Each 6SL7 contains two triode sections. The first valve comprises the input gain and the driver for the passive RIAA filter. There is an argument that passive interstage RIAA filters sound better than filters where one or more of the poles is positioned in a feedback loop. This view is particularly prevalent among the zero-feedback single-ended triode fraternity...
"What about the single-ended sisters?" demand plebs, stage left.
Sadly something of a minority sorority, quoth the old scribe. The consequence of this it that the RIAA passive filter lies between 6SL7 gain blocks. The passive filter between valves means the listener must beware thinking that sound balance difference is all due to the valves when it might be due to slight impedance differences affecting the interstage passive RIAA filter. Hence using the new valve in the first stage before the filter, where it will have less effect (anode, or plate, impedance being part of the basic valve spec) than in the second stage, where the grid impedance and parasitic capacitance (which are more widely toleranced in basic valve specs) may have more effect on the filter.
Valves are like cartridges or vehicle suspensions. They begin not working properly, then run in to good enough performance, and continue to improve gradually. They level off for most of their working life then gently deteriorate. Hence, fitting a new Ohlins on the back of my bike will always seem like an improvement on the old shocker, and in a few years time another new one would have the same effect. The same applies to pick-up cartridges. Because the valve electron emissions are the way they work, they gradually reach their optimum working condition. Grant Fidelity suggest 150-300 hours to burn-in, with most changes happening in the first 150 hours.
![[Shuguang Treasure 6SL7]](../jpg/shuguang_treasure_6sl7_circ2.jpg)
Out of the box the 6SL7 were therefore not expected to be up to snuff and your old scribe anticipated waiting a week of daily listening for them to break in. However, their initial compressed, bandwidth limited presentation opened up rapidly within 6 sides (4 of Little Feat and 2 of Sly Dunbar) to have your old scribe enthralled. They were already as good as, if different from, the custom TTM tested and matched Canor supplied (and individually numbered for location) Russian made modern Tungsol branded valves.
Having started by sounding like a cold solid state amp, within 2 hours they were sounding earthy and articulate in the bass, with the improvements gradually moving up through the audio frequency spectrum. The only reason to comment on a brand new valve in a review is to ensure that readers know they never sound as good fresh as when they have settled in. First the upper bass and ambience improved, while the midrange remained honky, drawing attention to Mr Dunbar's excessive use of disco syndrum whoops, having obviously bought one just before entering the studio to record Sly, Wicked & Slick. Treble began by being congested and 2-dimensional. Purchasers beginning on their tube-rolling odysseys beware misleading first impressions.
After a dozen on-off cycles and about 20 hours playing music while doing other things, your old scribe sat down to listen and establish whether some critical listening could begin, knowing this is at least 130 hours short of the recommendation. The system seemed to be sounding as good as it ever does so it seemed fair to believe that the two Shuguang Treasure 6SL7 were stabilised and ready for action.
It became quickly apparent that these valves were at least the equal of the Canor hand selected Electro-Harmonix 6SL7 valves. Canor have selected these for each position (they are individually hand numbered to match the numbers on the valve bases in their amplifiers) so the interlopers begin at a disadvantage.
The early impressions were of differences in substance and tangibility, rather than tonality or clarity. Before the plebs chorus accuse me of purple prose and pretentious wine-speak, and nominate me for Psued's Corner, your old scribe seeks to defend this position. The 6SL7 comprise two small-signal triodes in one glass envelope. Triode means three elements, so they have only cathode, anode and grid. The transfer characteristic of the valve is usually an S-shaped curve. If it is a more linear, the changes in voltage from anode to ground, via cathode, will better mimic the changes between grid and ground. If more linear near the toe of the curve, the valve will have lower distortion during quiet passages than loud, and if more linear near the top of the curve, the valve will excel driving hard during crescendoes. We're in class A here so, with a linear transfer characteristic, providing the power supply is big enough, clean enough and with a low enough impedance, all else should be well. The dynamic envelope which a valve can manage has minimum standards for any particular valve type but how linear the valve behaves towards the toe and the top of its operating range will depend on the designer's choices of materials and electrode construction.
The soundstage illusion is deeper and taller with the Shuguang than the Electro-Harmonix. At first it was a difference like the subtle difference between an American football (the Electro-Harmonix) and a Rugby Union ball (Shuguang Treasure). The former has pointy ends and a slimmer waist for long throws while the latter is plumper for passing and kicking. As the listening hours progressed, the difference increased, leaving the ball analogy way behind.
Switching from the moving iron MusicMaker II to the rebuilt Decca London the usual earth problems and RF interference had to be minimised before critical listening. Similar differences are heard with the Decca as with the MusicMaker II. The Decca has some advantages in bass definition and speed that are successfully exploited by the Shuguang 6SL7. Similarly the Decca's lack of cantilever improves timing and phase accuracy resulting in a deeper soundstage. The Decca's constant threat of sounding on the edge mistracking also became more obvious.
Changing the position of the Shuguang 6SL7 to the second stage of each channel instead of the input valve illustrates its handling of larger signals. Similar effects are heard to those heard when handling the tiny cartridge output signals. However, they are all to a smaller degree. This implies that the Shuguang 6SL7 excels at handling the handful of available electrons at these signal levels. It also demonstrates that input stages may often be more prone to the effects of tube-rolling. The input amplification stage of a phono pre-amplifier has the most challenging amplification task in audio. It is bad enough for microphone pre-amplifiers but when the RIAA curve is added to amplify any errors from the input stage, the phono-preamplifier challenge is even greater.
Shuguang have done it again with this Treasure series select version of the 6SL7. TNT-audio.com do not accept advertising and are therefore unbiased by advertising income. This may be the reason that many manufacturers seem frightened to submit equipment to us for review. We have been told by manufacturers that there are magazines expecting a minimum level of advertising space to be booked in order to secure a review. Neither TNT-audio.com, nor your Old Scribe, have any special arrangements with any manufacturers. Grant Fidelity and Shuguang have never shied from submitting samples to our critical ears, nor have they attempted to influence our opinion further than the usual brochure blurb. If it were not a review sample, the only reason I would remove this valve from my phono-preamplifier would be because it is too tall to put the lid on (it sounds better with the lid off anyway). The escalating price of NOS valves, driven partly by it now being a directly accessible market to the whole globe, means that it is once again viable to manufacture valves designed to excel in audio circuits. Wealthy audiophiles and musicians want ever better sound and there are manufacturers ready to resume valve production with a changed emphasis towards audio quality. Shuguang are such beneficiaries of the new Chinese approach to commerce and the improving global market for valves and we music lovers are the end user beneficiaries.
I have not heard a better current production 6SL7 from any manufacturer. NOS samples are too inconsistent to recommend. The 6SL7 double triode has always been one of the best choices for the tiny signals handled by phono-preamplifiers, typically achieving a low-noise transparency with a lush mid-band perfect for handling the human voice. The extra bass extension and bass definition of the Shuguang Treasure Series GF select (what a mouthful) would be enough to justify just over 200 bucks a pair in any phono-preamplifier over a grand. These 6SL7 samples add sharper transient-snap and timing too. The extra transparency and linearity that offers the greater scale and dynamics ices the cake sufficiently to justify two pairs, where possible, in a phono-preamplifier costing over 2000 Dollars or Euros. With valve equipment, the first tuning priority must be vibration isolation and the second tuning priority must be valve choice. With the tiny signals from phono cartridges, avoiding hum is an additional challenge, through careful earthing (grounding) arrangements and careful cable dressing. In a phono or microphone preamplifier, the 6SL7 is a great choice of amplifying device and the Shuguang Treasure 6SL7 may be the best of modern production.
| Music enjoyed while writing this rreview | Reference system |
|---|---|
on vinyl of course
|
Equipment used in this review:
|
Copyright © 2015 Mark Wheeler - mark@tnt-audio.com - www.tnt-audio.com
[ Home | Staff & Contacts | DIY & Tweaks | Listening tests | HiFi Playground | Music & Books ]