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REVIEW: Shuguang / SuperTNT 845M Tubes

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Model: 845M
Category: Tubes
Suggested Retail Price: $280/pair
Description: 845 metal plate tubes
Manufacturer URL: Shuguang / SuperTNT
Manufacturer URL: Shuguang / SuperTNT

Review by Ed Sawyer ( A ) on January 20, 2005 at 18:36:05
IP Address: 24.34.46.96
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for the 845M


The new 845M metal plate tube from Shuguang/SuperTNT

This review covers the new 845M tube, from Shuguang in China, and distributed by SuperTNT.com . Serial numbers for the pair in this review are 0002 and 0003, the first two in the USA, as far as I know. Retail price is $280 USD per pair, direct from SuperTNT in China. I do not believe they have a USA based distributor yet.

The 845M is a recent development by Shuguang, and structurally it is a very close copy of the 1940's vintage Amperex brass base 845, and also their recently released 845B tube reviewed previously. The most notable new feature which sets this tube apart from all other 845s is that it has a metal plate as opposed to a graphite plate. Yes, the Kron KR845 also has a metal plate, but it has a 10v/1A dull oxide-coated filament, and thus not really a 'true' 845 in all respects - true 845s all have bright thoriated-tungsten 10v/3.25A filaments. A beautiful copper base is hiding under a thin nickel plate (more about that later). Pins appear to be nickel-plated brass. Like the Amperex and 845B, it has no top mica connecting the plate structure to the glass envelope. (current production 845s from China, Kron and Cetron all have top micas which couple the plate structure to the glass. The 845B/845M are unique among current 845 production in this regard). These 845M have about 70% to 80% of 845 dissipation ratings (e.g. between 70 to 80 watts maximum dissipation) and 1250v plate rating and as far as I can tell are compatible with any 845 amplifier application, within dissipation rating constraints. Like all 845s (except Kron), these have Thoriated Tungsten filaments, which glow brightly. It has two ring getter halos at the base of the tube.



(Click any image for a larger version)

Build Quality

Internal construction is done to a high standard, definitely a cut above the normal Chinese 845 tube, and even a little finer than 845B. Welds and metal forming seem to be quite well done and accurate, no sloppiness from what I can see upon close inspection. The metal plate has extra 'wings' welded to it, to increase dissipation ratings. These, like all the welds in the tube construction, are done by hand. The metal plate itself and the wings seem to have different coatings/treatments - SuperTNT goes into this a bit more on their site, I believe. The metal plate itself also has oval cutouts along the sides of the plate, which let a lot of light escape. Between the reflectivity of the shiny metal plate, the lack of micas, and the cutouts on the sides of the plate, this tube gives off close to double the light of any other 845, and it looks like a million bucks. Very bright and mesmerizing to look at and will light up a room to a significant degree.

A minor issue: the bases on this pair have a very thin nickel (?) plating. I took them out to my shop to buff up the shine, and even just using the buffer with a very fine compound on a soft wheel was enough to completely buff off the plating on the base. Ultimately, this was fine with me since I like the look of the copper base better anyway. But users should be aware the plating on the base itself is thin, and could likely be scratched off with a bit of effort. It would be nice to see either thicker plating, or simply foregoing the nickel plating all together. I think the copper looks better anyway, and it would save the effort/cost of the plating.

Comparing directly to an old stock Amperex 845, the caliber of construction of the 845M is very good but not quite as precise. This is not surprising, given that in the old days thousands of these tubes were made by highly skilled workers who had been doing it for years, and the tube industry and its' body of knowledge was enormous compared to today. That Shuguang is able to do as well as they have, especially considering the issues surrounding a high-wattage dissipation metal-plate tube, is an impressive feat, considering this pair is one of their first production pairs released to the public.


Data sheet included

845B and 845M

845M and 845B, another view

Packaging

The packaging supplied with these is the best 845 packaging I have seen, better yet than the 845B packaging - quite robust, with a hinged box made from high-density mat board, and an inner 2-piece foam cushion and foam wrapper. These tubes came direct from China and survived fine with no damage - an impressive feat. The box has a nice foil imprinting on it, and is quite high caliber, easily equal to the quality of the boxes from botique european tube brands. SuperTNT also included a full readout on test results and op point data for each tube, a nice touch.


The Packaging

Nicely made boxes

845M tube

845M tube

Electrical Tests

Running these tubes on my curve tracer setup shows traces which are very well matched and clearly well within specs, as compared to other (vintage Amperex) 845s and the 845B. The curve tracer, A Systron-Donner 6200B, runs up to 1000v on the plate and negative grid steps from 0v to -100v on the grid. In both cases, the tubes had curves which were textbook accurate, even at the top and bottom. Electrically, they are perfect, as one would expect from new production tubes. Quality control on this aspect has no problems at all. They biased up fine in my amplifiers, each drawing near-identical current to the other, and spot-on where the 845B and other 845 tubes bias up. Running on AC filaments, they required some minor adjustment of the filament hum pot. With adjustment, residual hum was the same as other 845s I have been running, and a non-issue. Running on DC filaments of course there were no problems, with zero AC hum. These tubes do take longer to warm up than graphite-plate 845s, so instead of maybe a 5-10 minute warmup, they really need more like a 15-25 minute warmup to fully stabilize their operation point.


Curves, tube # 0002

Curves, tube # 0003

Curves, vintage Amperex 845 brass base

Sound

I ran these in my Electronluv 45-845 amps, I have the tubes for a month or so and have probably 100 hours on this pair so far. I compared to other 845s concurrently (one 845M in one amp, and another 845 in the other amp), and also comparing the tubes in pairs. Other amps included Antique Sound Lab AQ 1006-845, which were used but not as extensively. The Electronluv amps run these tubes in the 75-80% dissipation range (corrected from earlier review), approx 70ma, a nice high voltage sweet spot without over stressing the tubes by running them at max dissipation. Output power is about 18-20w, using a SET Parafeed topology. Using amps with adjustable bias (e.g. 'fixed' bias), one should be conscious of whether the amp runs the tubes within the dissipation rating. Fixed-bias amps will be able to rebias as needed, those with self or cathode-bias may have a bit less options in that regard. The good news is most commercial amps don't run tubes at 100% maximum ratings, for longevity's sake. Check with your amp manufacturer to be sure of the dissipation/op point, or measure it and calculate it. (plate voltage x plate current in ma = plate dissipation in watts. e.g. 1000v x 100ma = 100w ).

The 845M is a great sounding tube, unique among all 845s. It shares some family sound with the 845B, which is a good thing as that is a great sounding tube, especially considering cost. The metal plate adds some detail and seems to enhance the clarity of vocals. Bass is as good as a graphite tube, the mids and highs seem to sparkle a bit more and in general seem more clear, clean and unveiled. Its' a subtle difference - more of a flavor change than a night-and-day type of thing. However it is a unique sound and worth having a pair for that reason alone. Vintage 845 metal plate tubes are so rare as to be unobtainium in any reasonable sense of the word. I have a total of 5 (from 3 or 4 different brands/makers), after years of looking. Of those only 1 is really in superb shape. The others either arrived with broken filaments (common on vintage 845s, unfortunately), or have internal gas, or are otherwise unsuitable. Other than the ones I have, I have seen a total of maybe 4-5 other pairs change hands - usually sold in 'as-is' condition, for large sums and almost always selling to buyers in southeast Asia. A metal plate 845 has been held out as a holy grail of 845s for some time now, and the scarcity only serves to drive up the lore and interest in it. These 845M are a worthy successor to the throne of modern 845s, and it's good to see some unique developments in this regard, especially from up-and-coming tube makers in China.

The 845M are as non microphonic as any other 845 I have. (due to low gain, 845s in general are not microphonic to any noticeable degree, even with abuse like tapping the tube while in operation).


845M in operation

845M in operation, another view

845M in operation, another view

845M in operation, another view

Conclusion

Do NOS vintage tubes sound better? It's hard to do direct comparisons since nice pairs of metal plate vintage 845s are so hard to come by. The 845M enjoys a unique niche among the world of modern 845 production, one which will likely not be challenged for a long while, if ever. Considering the cost and difficulty in chasing the vintage metal plate 845, the 845M is a no-brainer if you are interested in that type of tube, and its' pretty much the only game in town. Vintage 845 (graphite plate types) do enjoy some improvements in sound over the modern varieties, 845M and 845B. That is not surprising, considering even small companies like United made thousands of 845s over their production lifetime, and hade fine-tuned the process to a high degree. That the 845M is as good as it is is high praise to the skills of modern tube makers and all 845 users owe Shuguang a debt of thanks for their efforts in this regard. SuperTNT has some more information on the teething issues they and shuguang experienced in developing the metal-plate 845 - it wasn't easy. They have these available for sale on their site now, as I write this. It is worth also reading their news and information regarding the development of the 845M and what goes into their test efforts to match and grade them.

I'd have no problem recommending the 845M to anyone who uses 845s, keeping in mind that one needs to check the dissipation rating to make sure it is ok. In my experience, if the tube is drawing too much current on the plate, you will see it. After shutting off the amp after an hour or two of use, look closely at the plate. There should be little to no reddish color, in a dark room with the amp just turned off. If you see color on the plate while the amp is running, then likely they are being run too hard, and it would be wise to investigate further. A pair of the prototype 845M which I have drew too much plate current, and the color was visible on the plate in operation, and very noticable after shutdown. They were dissipating probably 30+ma more than they should have been, however I did run them for a couple hours at a time this way with no ill effect. I am sure extended use in that manner would shorten the life significantly, so heed SuperTNT and Shuguangs recommendation on dissipation ratings.

No matter how high resolution the system, these 845M tubes will not disappoint sonically (or visually!), based on my experience with them. These are far and away the best tube made in China that I have seen and heard, and the only Chinese tube I'd use in my own equipment.

Associated equipment for this review:

  • Electronluv 45-845 monoblock amps
  • Electronluv AV20/801 preamp
  • Meitner-modified Sony SCD-1 cd/sacd player
  • Martin Logan CLS speakers
  • Cardas Neutral Reference cabling
  • Maple equipment stands by Terry Cain (amps, preamp) and BJ Tanner (CD player)
  • Vintage graphite and metal plate 845s from Cetron, United, RCA, GE, Taylor, Amperex, DeForest and others.



Product Weakness: Nickel plating on base could be thicker/better. That's about it!
Product Strengths: Unique in the market, metal plate 845 havent' been made in 70+ years. Excellent sound and looks, reasonably priced.


Associated Equipment for this Review:
Amplifier: See review
Preamplifier (or None if Integrated): See review
Sources (CDP/Turntable): See review
Speakers: See review
Cables/Interconnects: See review
Music Used (Genre/Selections): jazz, vocals, pop, standards, rock, etc.
Room Size (LxWxH): 16 x 21 x 9
Room Comments/Treatments: various DIY
Time Period/Length of Audition: 2 months so far
Type of Audition/Review: Product Owner
Your System (if other than home audition): See review




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Topic - REVIEW: Shuguang / SuperTNT 845M Tubes - Ed Sawyer 18:36:05 01/20/05 ( 24)