For those of you who are obsessive with things audio, like me, I've come up with a spreadsheet to help in determining how to match up the small signal tubes in your preamps.  The spreadsheet was originally intended for conrad-johnson preamps that use multiple 6922s in each channel but will work just as well for any preamp that uses 2, 3, or 5 identical type tubes per channel. 

I know that we often buy them as matched pairs to begin with but if you'd like to go one step farther these spreadsheets may be of some use. 

The spreadsheet looks at three characteristics: noise, Gm (transconductance), and gain. The idea is to arrange the tubes into position so that the left and right channels match the most closely on the characteristic(s) you think is (are) most important.

Each spreadsheet also has a sample of an actual matching I did for some Mullard PCC88s that I use in the conrad-johnson Premier 16LS2 just so you can see what it looks like. 

Not every vendor supplies all of these measurements but it came in handy when I recently purchased some unmatched Gold Lion 6922s from Jim McShane (review forthcoming).

I obviously have too much time on my hands. 

For 2 tubes per channel:  Zip Pr 17 Small Signal Tube Matching.zip 

For 3 tubes per channel:  Zip Pr 16 Small Signal Tube Matching.zip 

For 5 tubes per channel:  Zip ART Small Signal Tube Matching.zip 

As always, comments are welcome.

The review set was purchased from Upscale Audio which lists the price as $44.95 apiece.  These tubes were cryogenically treated which costs an additional $8 per tube.  The tubes have a manufacture date of September, 2010.  The set has many hours of use and did not change in tone as the review progressed.

The KT120 is a newly developed tube by New Sensor with a plate dissipation of 60 watts per tube.  In comparison, a 6550 is rated at 35 watts and a KT88 at 42 watts.    When used in an amplifier not specifically designed for the KT120, you won’t benefit directly from this capability but certain amps, such as the Bob Carver Black Beauty 305, do utilize the tube’s extra plate dissipation.  It is also claimed that due to the fact that the KT120 is running much under specification in most applications, there may be extended tube life as a result.

The New Sensor Tung-Sol KT120 has a three-hole grey plate structure with a top getter and two side getters extending near the center of the plates.  It has a chrome colored collar and black base.  It has been described by at least one writer as two 6L6 power tubes residing in one envelope.

This is a physically large tube so you should ensure:  1) the tube sockets in your amp have cutouts large enough to accommodate them and 2) if you use a tube cage, that there is sufficient clearance since they are taller than KT88s.  Also, please see my comments at the end of the review regarding the heater current draw of the KT120.

The small signal tubes used in the Premier 11A were GE JG 5751 black plates and GE 6CG7 of the older, white label vintage (these are not the tubes in the above picture).  The Premier 16LS2 preamplifier carried Electro-Harmonix 6922EH tubes outfitted with two conrad-johnson O-rings per tube.

Listening Impressions:

• Listening to the Haydn Piano Trios on DVD-A, the sound is smooth, easy on the ears and detailed.
• The bass response lays a solid foundation to the music and is one of this tube’s strengths.
• Dialogue is clear and vocals have good realism.
• Transients are average to good but lack impact.
• Soundstage and dynamic range are excellent as was evidenced on the Odyssey CD by Yngwie J. Malmsteen’s Rising Force.

I found these tubes better at rendering music, especially rock, than for video (DVD and Blu Ray) applications.  They were also very good when used in conjunction with my cable box to view TV programs and Netflix streaming. 

The NS Tung-Sol KT120 draws 1.8 amps of heater current per tube, so before you use them, you should check with your amp’s manufacturer to make sure the transformers in the amp can handle them.  Just as a point of information, the vintage Tung-Sol 6550 and GE 6550A also draw this amount of heater current.

conrad-johnson now supplies these tubes as standard equipment on their current line of amplifiers.  Messrs. Lew Johnson and Bill Conrad both think very highly of this tube and, in fact, believe it to be superior to the SED =C= 6550C.  From what I’ve read on the conrad-johnson forum at Audio Aficionado, this tube appears to be almost universally preferred by c-j users who participate there.

In the final analysis, while these are good tubes, and appeal to a wide audience, there are any number of tubes, both vintage and current production, that I prefer.  As always, your opinion is what counts and it will most likely be different from mine.

The subject set of six Electro-Harmonix 6922EH tubes was purchased directly from conrad-johnson design, inc.  The 6922EH has the typical Russian squat, larger bottle shape, “flying saucer” getter ring and steel pins.  Although they  are available in a gold pin version which should show a resistance to getting grungy, I don’t know if there any real sonic advantages to having them.  This set was manufactured in August, 2008.

6922EH front view                                                                             Flying saucer getter
     

According to the c-j web site:  “At conrad-johnson we spend countless hours evaluating various vacuum tubes for each product. The tubes are selected based on sound quality and reliability. We know of no currently available tubes that are reliable and will improve the sound quality of your conrad-johnson component.  All tubes that we supply are then tested in circuit for performance to our specifications. For consistent results, we recommend that you purchase tubes supplied by conrad-johnson.” 

Elsewhere on their site:  “Many of the newer CJ preamps and power amplifiers come with circular rubber tube dampers as standard. We recommend the use of these on all preamplifier tubes and on amplifier input tubes. Avoid using the very soft Sorbothane tube dampers that have been commercially marketed. These melt from the heat of the tubes and can foul the tube sockets. Do not use any kind of damper on amplifier power output tubes.”

Review set with rubber O-rings in place
 

These quotes are cited to explain why, contrary to my usual practice of using older production tubes, the subject tubes are the ones actually supplied by c-j and the stock O-ring tube dampers were used.  It’s recommended that the two O-rings per tube be placed approximately 1/3 of the way from the top and bottom of the tube.  Quite honestly, I think there are better tubes out there and that the O-rings, while of some benefit, change the sound of the component in some ways that I don’t care for.

That having been said, there is the counter-argument that using the tubes a component was voiced with and in the manner that they were intended to be used (i.e., with the tube dampers), gives the listener the opportunity to hear the component as the manufacturer intended it to sound.  Also, in defense of c-j, the tubes I’m referring to, that I think are superior, are old stock (used, ANOS, and NOS) and therefore in limited supply and sometimes, much more expensive.  An audio manufacturer needs to ensure that their customers are able to purchase a ready supply of replacement tubes.  The 6922EH fit that bill.

I’m in the process of having my c-j Premier 140 amplifier repaired and while it’s in the shop, the capacitors are being replaced with the newer CJD Teflon jobbies.  According to both reviewers and c-j owners, these Teflon caps take an inordinately long time to break-in.  Estimates range from 300 to over 1,000 hours before they are fully settled-in and their true potential is realized.  With that long time period in mind, I’ve decided to use the 6922EH dual triodes in preparation for, and during the break-in period.  Although not exactly cheap when purchased from conrad-johnson, I figure I’d rather burn these than NOS Bugle Boy 6DJ8’s which are going for $110 to $130 each nowadays.  Plus, using them while I still have the 11A on line gives me a basis for comparison when the Premier 140 finally does come home.  

The Listening Impressions portion of the review is based on using the following output tubes in conjunction with the 6922EH:  New Sensor Gold Lion KT88, Ei KT90 Type II and New Sensor Tung-Sol KT120.  The small signal tubes in the Premier 11A continue to be my currently preferred configuration:  all General Electric of the older white label type.  They are the GE JG 5751 black plate, triple mica with a D-getter and the GE 6CG7 grey plate, double mica with an O-getter.  Years of manufacture are unknown.      

Listening Impressions:

• The sound of wooden blocks and percussion is excellent.
• Rock music through the Ei KT90’s is forceful and detailed.
• Female voice varies in quality depending on the output tube, suggesting these are very accurate in that range.
• More extended in the upper frequency range.
• The sound stage is not as consistently deep as the Bugle Boys.
• Not as grain-free as the Amperex tubes.  Although that is a hallmark of the Amperex brand in this tube family.
• A little less of the emotional content and musicality in comparison to the Amperex Bugle Boy 6DJ8s and 7308s are conveyed.
• The match with the NS KT88 is better than the Amperex Bugle Boys in terms of overall clarity and macro-dynamics.

Although the 6922EH may not be among my favorite dual triodes for the Premier 16LS2, they did allow for clear differentiation among the output tubes.  I’ve previously referred to the chameleon-like quality of the Premier 16LS2 and in this respect, the 6922EH are able to show that characteristic of the preamp about as well as any tubes I’ve used. 

I haven’t used any currently produced tubes in the 16LS2 other than these so I cannot draw any comparisons to either the New Sensor Gold Lion 6922 or the JJ brand.  I can say, however, that the 6922EH “speak” with a clear and neutral voice.

These reissues of the original Genalex KT88 are manufactured by New Sensor in their Saratov, Russia plant.  They have a double top O-getter with one additional O-getter on opposite sides towards the top portion of the plate structure.  The Gold Lion has a chrome-colored collar and brown base.  The tubes feel hefty in your hand and have an attractive appearance.  Not that we’d let their appearance affect our feelings regarding their sonic characteristics. 

They were purchased as a lightly used quad (< 100 hours) from a private seller.  As a result, they did not change character during the audition other than when (see below) the tubes in the Premier 16LS2 were replaced.  They are available online from many vendors including Jim McShane at $54.50 each and Upscale Audio for $59.95 apiece. 

During the first part of the audition, the Gold Lions were used in conjunction with Amperex Bugle Boy 6DJ8s in the conrad-johnson Premier 16LS2 preamp and for the latter portion, the preamp was inhabited by Electro-Harmonix 6922EH wearing their conrad-johnson supplied O-rings.  The Bugle Boys, during their stay, were ring-less.  The primary difference in how the Gold Lions sounded when used with the two types of small signal tubes is noted in the Listening Impressions section.

Let me break with my usual practice and say right up-front that the New Sensor Gold Lion KT88s are my favorite tubes with the exception of the vintage Tung-Sol’s previously reviewed.  I need to buy another quad for when I get my Premier 140 power amp back from conrad-johnson where its being repaired and having its capacitors upgraded to the CJD Teflon versions.

Listening Impressions:

• Macrodynamics, especially with the 6922EH in play, are excellent.
• Lower bass (at least as low as the speakers are capable of) could be more prominent.  Although what’s there is tuneful and never one-note.
• While listening to the Come Away With Me SACD by Norah Jones, she is a physical presence in the room.
• The violins on the 7 Concerti for Woodwind and Strings CD are sweet and feathery sounding with abundant detail.  You can immediately recognize the “Archiv” sound which I find to be a little tipped-up in frequency response.
• In comparison to the Tung-Sol 6550 black-plates on the same CD, the Gold Lion’s are a little quicker, lighter, airy and bouncy.
• There is a solid central image with excellent projection into the listening space.  Depending upon the source and the material, it extends to this listener’s seated position which is about 8 feet from the plane of the speakers.  When I wasn’t hypnotized by Charlize Theron, the Aeon Flux DVD was an exercise in sound field immersion.
• Lateral separation projects beyond the outside boundaries of the QUAD 989’s and together with sound stage depth, are reference quality.
• On the Into the Labyrinth MFSL LP by Dead Can Dance, the sound is quick, taut, with details not heard on my CD and with a cavernous sound stage to boot.

The New Sensor Gold Lion KT88’s are, in my opinion, a total success and sound almost identical to their predecessors, the GEC KT88.  If anything, the New Sensor version may be slightly more fleet of foot and on any given day, my judgment of which sounds “better” is going to change. 

Of all current production output tubes that I’ve auditioned, these are undoubtedly my favorites.

This is the final installment (at least for now) in the vintage Tung-Sol 6550 series of reviews.  This set is comprised of the top getter only version of the tube.  The subject tubes are the earliest black plates of this type produced.  This was followed chronologically by a single top getter with a single side getter comprised of two D-shaped getter rings and the final version of a top getter plus a side getter on either side of the tube.  In this final version, which was retained by the subsequent solid grey plates and three hole grey plates, the getter rings were O-shaped.

Three of the tubes in the sample set have the number “5” below the octagonal 6550 stop sign on the tube’s top.  All the other Tung-Sol 6550’s that I own have the number “3” below the stop sign and this may be a distinguishing characteristic of the earlier tubes.

Listening Impressions:

• The bass character may sound, initially, somewhat lightweight until you realize how accurate and musical it really is.  At sufficient volume, the bass strings vibrate so cleanly you visualize them moving in space.
• Liquid vocals with the emphasis on the throat and mouth and relatively less on the chest of the singer.
• Voices during dialogue sound like real people talking with little artifice.
• Bamboo rods and wooden blocks are excellent but not the best I’ve heard.  The GEC KT88 set the standard, in my opinion, in this regard.
• Reference quality timbre, decay and dynamics.
• Extended, but not strident, treble with delicate transients on instruments such as acoustic guitar.
• Piano keys tinkle (okay, stop sniggering).
• Wide and deep sound stage populated with solid images.
• The emotional content of the music is conveyed beautifully with the oboe sounding sad and plaintive in the Concerto for Oboe in C Major from the 7 Concerti for Woodwind and Strings by Antonio Vivaldi.
• The black plate Tung-Sol’s and the Bugle Boys reinforce each other’s extremely natural and musical sound qualities.

You find yourself listening to the music rather than to your system.  As I found with the other two vintage Tung-Sols, the black plate version may be bettered in certain areas by other power tubes.  However, for an overall consistently excellent sound, nothing surpasses the Tung-Sol 6550.  And within this family, the black plate version is the ne plus ultra for a natural and musical presentation. 

The XLO Ultra 1 interconnects under review today are a half meter long, made from 99.994% pure OFHC copper and consist of six stands per positive and negative in each cable.  The interconnects are constructed with a Teflon central tube, insulation and wrapper.  The strands meet at a right angle with the black strands wrapped over the lavender ones – the lavender conductors are, in turn, wrapped around the central Teflon tube.

Price is $185 terminated with XLO’s nonmagnetic, gold plated RCA connectors.  The interconnects are relatively flexible, skinny, and therefore easy to work with.

For some reason, the barrels appear to be blue in these photos but are, in fact, lavender in color.

This review should be read in tandem with that of the Amperex Bugle Boy ECC88 6DJ8 dual triodes.  The reason for that is they seem to form a synergistic union when used together.  Initially, the Premier 16LS2 preamp was outfitted with Amperex JAN 7308 green label tubes.  The 7308’s were not complementary to the Ultra 1’s, as the Bugle Boys later proved to be.

These interconnects replaced a set of Shunyata Antares, 1 meter single-ended interconnects which retailed for $2,000 when new.  So at least in terms of price, the Ultra 1’s had some very large shoes to fill.  This could very well be a case of Keds sneakers taking on Manolo Blahnik.

Listening Impressions:

• Volume levels need to be raised two or three clicks (1.5 dB to 2 dB) in order to give the same perceived sound levels as the Antares.  See comments in the concluding section as to why this may be the case.
• The sound is relatively clear and somewhat lean.
• Not as smooth, rich or dimensional as the Antares.  However, once the Bugle Boys were brought into the picture, the Ultra 1’s approach, but never quite reach, the degree to which the  Antares exhibit these qualities when matched with the Amperex 7308’s.  The Antares/Bugle Boy combination, however, is decidedly in a different class and at 11 times the price, should be.
• Bass response is well articulated and tuneful but not as deep as with the Antares.
• Voices are clear and massed vocals allow for distinguishing individual members.
• Good initial transients and music exhibits a pleasing quickness.
• Cymbals shimmer nicely but decay a little too quickly even with the Bugle Boy 6DJ8’s in the mix.
• The soundstage although foreshortened, is clearly delineated left-to-right with smaller, more compact images.

It may be that the unaccentuated midrange, lesser resolution and smaller images resulted in my compensating with a slightly higher volume level.  (Thank you, John, for providing this insight into why I was doing something but couldn’t explain the reason on my own.)

If you’re looking to add some punch to your system and these cables fall within your budget constraints, they are a worthy choice. 

The following is taken from Vacuum Tube Valley Issue 7 in an article penned by Eric Barbour © 1997.

“The 6DJ8 was introduced in 1957 by Amperex, the American division of Philips.  It was developed by Philips in Holland, under the European standard designation ECC88, and intended as a cascade amplifier for television VHF and UHF tuners, nothing more…The 6DJ8 became a popular type, especially when the engineers at Tektronix discovered it.  They found that it was consistent enough for their oscilloscopes, and gave excellent pulse fidelity….For many years Amperex/Philips was the major source, with Siemens, Telefunken, GE and Sylvania weighing in with their own versions later.”    

And that concludes our mini-history lesson on the origin of this tube-type.

The sample set was purchased as part of a larger group of 10 Amperex Bugle Boy ECC88/6DJ8 tubes and all bear the same GAA Δ5H2 manufacture and date codes of August, 1965.  These are the small O-ring type from Heerlen, Holland.

These tubes have been used extensively before and as such, did not change character over the course of the review.  The tubes installed previously in the Premier 16LS2 preamplifier were the Amperex JAN 7308 green label type and the reader is referred to that review as background. 

In addition, the reader should view the XLO Ultra 1 Interconnect installment in tandem with this one to get a more complete picture.  My apologies for any content redundancies in the cited postings.

Listening Impressions:

• When compared to the Amperex 7308 green label:
  • Detail is excellent but not quite as sharp
  • Bass lacks some energy
  • More midrange warmth and presence
  • Tonally not as neutral but more atmospheric and in some ways more realistic
  • The soundstage projects more often and further into the listening room with larger images
  • Dynamics may be a little reined-in with less impact
• Bells ring with clarity and decay as slowly as the recording allows.
• Treble is clear but not accentuated.  Violins are sweet, smooth and extended.
• Extremely natural sounding with an immediate involvement in the music.

As stated earlier, Amperex/Philips were the first to develop this tube and, in many ways, I do not believe that anyone else has done a better job at communicating the essence of the music. 

Moving backwards in time, this review covers the Tung-Sol solid grey plate tubes manufactured between 1960 and 1963.  The matched quad of output tubes under review were made in August, 1962 (3226236-3).  They have the hallmark ST bottle shape with a top getter and two side getters projecting from the upper half of the plate structure.  There are four hexagonal, transparent mica spacers holding the transparent splatter shield and they have a chrome-colored collar with a brown base.

The tubes were OEM (original export manufactured) for Stromberg-Carlson, a telecommunications equipment and electronics manufacturing company, who, in turn, packaged them for sale to General Dynamics.

.          

The set is well broken-in and has seen hundreds of hours of playing time prior to review.  Although these tubes exhibit the usual Tung-Sol 6550 “house sound,” they are not identical sonically to the three-hole grey plates previously reviewed.  The Listening Impressions section that follows will, therefore, highlight these differences.

Listening Impressions:

• The overall presentation is smooth, refined and extremely natural.
• Detail is reference-level with sharp and clear initial transients.  Steel guitar strings zing.
• Percussion instruments played by slapping the hand against the drum head are almost life-like.
• Images are larger but not diffuse.
• The ocarina on American Acoustic by Tingstad & Rumbel is piercing without being shrill.
• Dynamics are borderline reference quality.
• Sound stage cues are easily apparent.  I was able to tell depth differences depending on whether the vertical venetian blinds behind my listening seat were in a closed and flat position (less depth) or closed but perpendicular (more) to the glass patio doors.

As you may be able to tell, these are among my very favorite output tubes.  While listening to the CD entitled Chet (the Keepnews Collection version) by Chet Baker, the only thing missing was a very cold vodka martini.

Tung-Sol Electric Inc. made the three-hole version of the 6550 output tube from 1963 to the 1970’s and it is the final iteration of this type manufactured by them.  The quad of tubes under review all bear a “322RM-3” manufacturer and date code.  I have never been able to decipher their alphabetic dating scheme and so I’m not sure exactly when the review set was manufactured.  The “322” portion of the code indicates that they were made by Tung-Sol.

This is a three getter output tube with one top getter and two on opposite sides near the top of the plate structure.  Tung-Sol utilizes four clear mica spacers around the tube’s top portion and the splatter shield is also transparent.  The tube has the classic Tung-Sol ST shape, a chrome-colored collar, and brown base.

Tung-Sol 6550 three-hole grey plate                                                          Top view with original box
      

Review set                                                                                               Close-up
     

The review set was originally purchased as two pairs c. 2004, most likely from E-bay.  They have seen hundreds of hours of play time since purchase and are therefore well broken-in.  As a result, there was no change in their sound other than what occurs during normal system warm-up.

An ergonomic aside:  the tubes snapped into place as if the sockets had been made specifically for them.  Too often the output tubes fit more loosely than I’d prefer or feel as if they’re being forced into place.

A Little History:
The 6550 output tube type was first developed by Tung-Sol and was introduced in 1955.  The first three iterations had black plates and were in order of development:  top getter only, top plus one side getter, and finally, top plus two side getters.  Next to be introduced were the solid grey plate version and lastly, the three-hole type under review.  The consensus is that the best were produced first and that as time went on and the plate structure changed, each succeeding generation was not quite as satisfying as its predecessor. 

Personally, I think they all have their unique charms but that’s for another discussion.   

Listening Impressions:

• Bass is solid and well articulated with no overhang or bloat.  GE 6550A’s have a reputation for their bass reproduction but I’m not sure what, if anything, they have over these T-S 6550’s.
• Dynamic range is excellent.
• Midrange is clear and neutral with dialogue easy to understand and vocals sounding natural.
• The treble range is delicate, refined and extended without being tipped-up and exaggerated.  Harpsichords are delicate without being threadbare and you can hear the strings resonating within a wooden body.
• Silences are black – the music just stops.
• Sound stage is wide and deep.

Vintage Tung-Sol 6550’s, the three-hole grey plates included, are not my reference output tubes, in both the c-j Premier 11A and the Premier 140, because they possess a handful of reference-level sonic attributes.  Rather, it’s the fact that they are consistently excellent across the panoply of characteristics a reference-level tube should have:  evenness of frequency response, low level detail due to vanishingly low noise, excellent transient attack, decay, inner detail and truth of timbre, a dynamic presentation, a fully-fledged sound stage populated by realistically scaled images, and an unassuming quality that allows the music to flow and connect with the listener without drawing undue attention to itself.

Other output tubes best the Tung-Sol in some of these attributes but none, in my opinion, have all of them to the degree that the Tung-Sol 6550’s enjoy. 

In keeping with the recent green ink theme, I switched out the white label GE 6CG7’s in the Premier 11A for Sylvania 6CG7’s.  These are 1958 vintage tubes, with triple mica grey plates and D-shaped top getters.  The tubes were purchased approximately eight years ago from Jim McShane and have seen considerable use in the past.  At the moment I have not seen them for sale, anywhere.

The 11A amplifier runs its output tubes in a push-pull configuration and its output stage is described as ultralinear.  The amp uses the 6CG7’s as phase inverter/output drivers.  These are the original, 6CG7 version of the tube with a central electrostatic shield that is said to reduce noise between the plates.  The 11A does not ground pin 9, however, so the tube operates essentially as a 6FQ7, which lacks the electrostatic shield.  The 11A, in fact, has “6FQ7” as the tube identifier for these two tube positions.

 Sylvania 6CG7's on the batting in which they were wrapped                               With original box
            

Central electrostatic shield                                                           Close-up showing D-getter
                       

 Box with tube wrapped in batting
 

Listening Impressions:

• Deep bass response.  Drums are taut and resonant.
• Percussive sounds such as wooden blocks are less realistic than the GE 6CG7’s, but not a day and night difference.
• Very good timbre and decay.
• Nicely extended treble with sharp leading edges.
• Larger image size with a more diffuse sound stage than the GE’s.

All in all, these are very nice sounding tubes that I could easily live with.  However, I do prefer the GE 6CG7’s in the system’s current tube and equipment configuration.