Review: JJ ECC83S short plate 12AX7

 

To be honest my expectations for this 12AX7 was low.  I haven't had a JJ tube in any of my gear for well over a decade.  Nothing personal, mind you, but back then I was all about more exotic tubes like the C3m, 5687s, EL156s, and whatnot.  JJ has been around since 1994, built on the ashes of Tesla and Ei.  Their small signal tubes aren't mentioned all that much on the forums I visit, or at least I missed the posts.

This particular version of the 12AX7 looks to be based on the famed Telefunken ECC803S, which also had a Tesla copy.  The architecture has small plates that are very similar to a 6DJ8.  This should translate to low microphonics.

As for the sound, at least as the gain tube for a power amplifier, the JJ ECC83S was better than I expected.  There is an overall darkness, making this a good match for some zingier MC cartridges or digital front ends.  This is a "chocolate" expression of the music, with solid and tuneful bass, warm mids, and a high end (to my older ears) that is even less detailed than a Mullard. 

Inner detail with the JJ is less than the long plate Mullard; a slight smearing of instrument and vocal space along with soundstage depth.  Nonetheless at least the JJ sounds like an vacuum tube unlike some of the inexpensive Russian offerings I've heard.  So, much like the TJ and the Psvane, a solid offering but, and your mileage will vary, not exceeding the better old stock versions of the 12AX7 I've heard.

Review: a Frankenstein Eico ST-70 tube amplifier

 I bought this strange modified amplifier on Ebay. It looks as if someone took a stock integrated and modified it to be a basic power amp. Gone is the normal set of controls on the front plate, replaced with a generic black panel and power indicator light.

 

A peek on top of the grille - what is inside?

Of course you know - you read the title of this post! Someone took an Eico ST-70, removed the preamplifier portion and converted it to use 5881s instead of the stock 7591s.

Since I didn't have any 5881s on hand, I modified this amplifier to use the military 6AR6. Since the 6AR6 has a completely different pinout (and bias points!) it took an entire rewire of the output stage, along with more negative bias than the stock circuit.

I also changed the power supply with new electrolytic capacitors for the main bucket, 6SN7 phase-splitters, and 12AX7 input tube. I also added a little 1.5H Dynaco choke to reduce the B+ ripple. After a little troubleshooting, and bias modifications, I finally got this amp to work; with 40mA per output tube. 

So how does this pentode output Frankenstein weird output tube sound? Even with old Russian 6N8S tubes, surprisingly good. Bass extension - with the large output transformers - is really deep. And there is the old tube midrange and smooth treble thing happening. Maybe it's been too long with an SS (Aleph J clone) amplifier, but this little push-pull tube amp is quite magical.

Chet Baker Sings, for example, really is holographic - for a mono recording - with his voice and trumpet sounding natural and forward. Compared to the Aleph J solid-state amplifier, music is more relaxed but, at the same time, more dynamic. The tube amplifier sounds way more powerful than its approximate 30 or 35Ws per channel.

I'm surprised that the KEF R500s work so well with this vintage Frankenstein; you never really know what you are going to get with modern speakers.

Once I get over the excitement of having a new amplifier, I plug in some old Zenith 6SN7s that I have on hand. Maybe things will get even better-better.

 

 

Review: The Audio Research SP-8 preamplifier

 

History: Audio Research has a long and, dare I say, storied past.  Back in the era when vacuum tubes where being consigned to the ash heap of history, they, and a just a handful of manufacturers were still making gear that used these ancient amplification devices.  Even in 1990 I remember being at a used electronics company in Colorado and receiving less-than-kind words when inquiring if they had any tubes or tube gear.  "Vacuum tubes?  Why would you want to use tubes?  Are you fixing an old piece of equipment?"

William Z. Johnson obviously didn't get the message,  Like so many afterwards, he started out modifying Dynaco gear, and branched out making his own equipment under the banner of Electronic Industries.  This latter became Audio Research which started with the SP-1 preamplifier and the Dual 50 amplifier.  They really didn't have a hit on their hands until the venerable SP-3A preamplifier, and D-70 plus D-115 amplifiers (and the various following iterations) came and made them serious contenders in the audiophile world.  They also dabbled - and still do! - with solid-state equipment but are, of course, really known for vacuum tubes.

The Audio Research SP-8, first introduced in 1981, went through several minor redesigns.  I tend to think of the circuitry as being the ultimate Dynaco PAS or Marantz 7. For example the phono amplification is done through a pair of 12AX7s with a 6DJ8+FET cathode follower, RIAA handled via the negative feedback loop.  The linestage is similar with a pair of 12AX7s and a 6DJ8+FET cathode follower with loop feedback.  Where Audio Research shines is the power supply.  In this case a solid-state regulator makes sure the phono state receives a dead quiet high voltage.  And, oddly enough, a combination of a 12BH7 and 12AT7 provide the regulated supply for the linestage.

Controls are fairly simple but with some older ideas that have gone out of fashion.  ie, of course there is a volume but there is also the increasingly rare balance control.  And something else - there is a stereo, mono, reverse, left, and right mode.  Add in the switchable AC outlets for that extra vintage feel.  There is, however, no tone controls or a loudness switch.  But one can mute, select the phono or four other line sources, and switch between tape out monitoring or input.

This particular SP-8 under review is a Mark II, Revision 5, and has only had three previous owners.  When my friend offered to sell me this well-known classic, I jumped at the chance even though it needed to be repaired.  It turned out, due to years of being in storage, the power supply section that handles the muting and 12AX7 filament voltage was no longer working.  Instead of troubleshooting it myself, I sent the unit out to the Audio Research service department, who still does repair work on this 30+ year old gear.  They not only repaired the power supply in question, but also cleaned the volume pot, replaced all of the electrolytic capacitors, put on new feet, and found an additional issue with the linestage that needed to be fixed.  Now this SP-8 is ready to provide service for many more years of service.

 

First Impressions: After unboxing the returned SP-8, I first had to figure out where to place the eight different tubes.  It isn't obvious since the circuit board is not marked.  Instead one has to look at the manual, figure out what version you have, and then double-check your work.  I'm glad I did because I had to swap the location of the 6DJ8 and 12AX7 in the phono preamplifier.  Luckily I did not power on the unit!  After switching the location of my two turntables, due to the interconnect lengths and phono input location, I was finally able to sit down and do some quick listening.

With new electrolytics and NOS tubes that needed to be broken in, I found the bass rather lightweight.  The top end was also bright and the midrange was a bit muddled.  Nonetheless I could tell there was an increase in detail over the replaced Classe Five.  I let the preamplifier cook for a few hours and things started to snap in place.  For example, Chet Baker's voice on the title song from the album She Was Too Good To Me, was very emotional; perhaps the closest one could get to the now deceased trumpet player.  Pink Floyd - The Wall had fantastic imaging without any blurring of the instrumental or voice outlines.  The Classe Five, in comparison, sounded a little darker and less forward.  The SP8, at least with the excitement that new gear brings, seemed to be a real step up in fidelity.

Listening Test: After a few days of background music duty, it was time to put the "new" Audio Research through its paces.  I could tell right from the get-go that the bass had become more extended and some of the forwardness had been reduced.  Note that tube selection will, of course, change the sound.  ie, a set of new production tubes may not be as satisfying as some original 1950s Mullard 12AX7s that I was lucky enough to have on hand.

I have an interest in electronic instrumental music, to the point where I have made my own albums.  For this review I didn't have the ego to listen to my own work but instead picked out the soundtrack Beyond the Black Rainbow by Sinoia Caves.  This has a heavy Tangerine Dream influenced album with one or two sequencers often going at once.  The SP8 did an extremely good job capturing the attack of the electronically produced notes, putting them into their shifting artificial space in the soundstage width.  Bass was also deep without any "classic tube" coloration or overhang.  This is no golden-hued Dynaco PAS experience but instead has a speed that, until now, I thought was impossible with the 12AX7 tube.

 

Neil Young's Tuscaloosa is a live album from his Ditch Trilogy days, starting with two acoustic numbers before the whole band takes the stage.  With the Audio Research his voice had a real presence, the body and the diapraghm can be heard projecting much like the "real thing".  I've done sound for a few live shows and this albums captures that experience quite well, also with the proper amount of hall/stage reverberation, along with the oddly recorded, cardboard sounding drums.  Likewise with the dynamic shifts, which were recorded in a honest way, capturing what it must have sounded like being there; provided you had access to the soundboard instead of being in the back row!

Imaging and soundstage depth was among the best I've heard in my system .  An example of this is the song Warm Ways on the self-titled Fleetwood Mac album.  This is a busy mix but the outlines of the instruments and voices weren't slightly blurred like lesser preamplifiers.  This led to more detail, or, as Audio Research would say, High Definition.  I've owned plenty of other preamps in my life but none have quite approached the sound of the SP8, which, given it's rather pedestrian signal circuitry, a real surprise.  It's neither dark nor bright (tube dependent, of course!) but seems to pass the sound from the Thorens TD309 turntable along in a refreshingly honest way.

Dead Can Dance albums, by some strange miracle, are usually very well-recorded.  My original 1994 UK pressing of Toward the Within is no exception, capturing the vibrancy and the crowd excitement of this live recording.  The song Sanvean, with Lisa Gerrard's voice taking center stage, is a beautiful tear-inducing song.  I was swept away by the emotion of her voice, proving that the Audio Research is no clinical piece of gear.  The depth and power of the music was, once again, presented very naturally without any undue added coloration that one would find in a vintage "warm" preamplifier, but neither did the overall sound swing the other way towards hyper-detailed iciness. 

Parting Thoughts:  Given the age of this preamplifier, it may be a surprise to many that I find it quite neutral.  However I look at this era, the late 1970s to the late 1980s, as a golden age of audio reproduction.  Yes there were fewer companies back then, but they were really pushing the envelope of technology.  There are many examples of this - Krell, Mark Levinson, Threshold, and, of course Audio Research.  The SP-8 is the sound of a classic 12AX7 feedback circuit taken to the extreme.  And it pays off - given the right tubes! - with a very neutral, high definition sound that is also transparent.  If you can find one, and have the patience to have it properly serviced, then the Audio Research SP8 is worth the trouble, especially if you are into vinyl reproduction.

I had to add the caveat about vinyl reproduction because of the high gain nature of the linestage.  The average CD player or DAC with a healthy 2V output will give one a very limited volume control range.  An example of this, with my second turntable, a Dual CS5000 and the Schiit Mani phono preamplifier.  I had to set the latter to its lowest gain setting - 42dB - otherwise the SP8 at the bottom of the detented pot mean I was only two click away before the music became too loud.  And this with an amplifier that is not particularly sensitive.

Review System:
Thorens TD-309 turntable with Ortofon 2M Bronze
First Watt Aleph J clone amplifier
Cardas Iridium interconnects
KEF R500 speakers with Cardas Twinlink speaker cable

Project: Restoring a Audio Research SP-8 preamplifier

 A recent purchase was this Audio Research preamplifier that sadly is in need of repair.  All original early 80s, it will need a cap job, a new volume control, and a solid-state regulator supply fix.  More later!

Project: Building the Pass ACA Amplifier

 

The ACA amplifier is a Nelson Pass design created to teach basic concepts about amplifier design. It is low-powered (6-8Ws per channel), run in pure Class A, capacitor coupled on the output, and is even single-ended.

There is a long, and very detailed article from Mr. Pass which, to put it bluntly, far surpasses my more vacuum-tube orientated knowledge. I see a single jfet driving a current sourced Mosfet, capacitor coupled on the input and the output, along with some modest feedback.  Anyone who wants to know the nitty-gritty of this amplifier should take a gander at the link for more information. For those who are a glutton for punishment here is the schematic:

 

My own requirements are modest wattage and an attempt to capture some of the magic that I hear with single-ended tube amps. The ACA amplifier can also be bridged, via an XLR input, to double the power, something I will need with my 86dB efficient Wharfedale speakers that are in a moderately sized listening room.  I won't need gobs of power for reasonable listening levels. Since my Classe Five preamp has XLR outputs, I will be going this route, building two stereo amps to use as bridged monoblocks.

Enough babbling - let's get building the first amplifier:

Here you can see the passive parts and the circuit boards. It's best to populate the small parts first - the resistors, followed by the caps and solid-state devices.

Once the circuit boards were stuffed it was time to start assembling the amplifier chassis for PCB fitment, along with RCAs, XLR, switches, and binding posts.

Here you can see the stuffed circuit boards attached to the heatsink. The Mosfet outputs are mounted too.

And I did some more work on the back panel, which has all of the connections.

Powering up the amp for the first time is always exciting. But I ran into a snafu - the power indicator LEDs would begin to flicker. Measuring the voltage from the power supply brick, I could see it was fluctuating from 24VDC (good) down to 5VDC (bad). A check on the DIY Audio forum indicated this is the lap top power supply going in protection mode if there is short.

To troubleshoot I removed a power supply lead from the boards, one at a time.  Once I found the board with the problem, I disconnected it from the heatsink. And then the problem went away. This was a clue that there was something wrong with this board.  I ended up having a cold solder joint that was easily fixed.  I guess those years of point-top-point wiring has come back to bite me.

Here I am biasing the output mosfets, each side set to 12V:

And then once that was done, I was able to - FINALLY! - give it a listen:

Initial Impressions: lower gain than the old workhorse Adcom 545. Instead of 9-10 o'clock on the dial, I have to turn up the volume to 1 o'clock to get the same sound levels. The ACA is very smooth, a little lacking in bottom end thump but still very articulated. Jazz - like Chet Baker's album Broken Wing - sounds fantastic, while harder rock albums seem to lack some of the macro dynamics. Of course we are only talking 6-8Ws here with 86dB Wharfedale speakers (6-ohm impedance) so not an optimal match. I wouldn't say the ACA sounds like a tube amp - some similarities: with a non-fatiguing top-end - but it also doesn't sound like your stereotypical SS amp either. Obviously some break-in may also be needed.

Luckily the second amp was a lot easier to build, taking almost half the time and with no problems to troubleshoot.

In this picture I still have to install the front power indicator LEDs and the top and bottom part of the chassis, but I did manage to listen to them bridged, using the XLR output from my Classe Five amplifier. Very impressive.  Neil Young - Live the Cellar Door sounds good on just about any stereo I've owned, but this may the best I've heard it, even compared to the days when I had an all tube chain and big UREI 813A speakers. Lots of micro dynamics, very realistic, and engaging. The amps sound way more powerful than the 12-16Ws it is making.

Some further listening - The Bee Gees - Trafalgar - revealed a slight metallic sheen that seemed to fade with further break in. Very clean but not lean. Detail, studio reverb, etc was all there. Frequency response was very even, no warts, and less "lossy" than some of the lesser tube amps I've owned. Single ended Mosfet is interesting, to say the least, not quite tube-y, nor is it "classic" solid-state (whatever that means). Just different, even more so than Class T (Tritpath) designs I've built. The old, and much need of a recap, Adcom 545, when put back in the system, sounded more indistinct, gray, and uninvolving, though it does have superior deep bass reproduction (and better damping and more power).

Gain is still a bit lower than I would like. Deep bass isn't as prominent as other amps, but again, 6-ohm and fairly inefficient Wharfedale speakers with 5" woofers here.


Listening Update: After a few weeks in the system, I'm quite impressed.  Very neutral with a touch of sweetness.  Some of the best depth I've heard out of a solid-state amplifier, along with very good detail retrieval.  Some of the better tube amps I've build or owned are slightly better at separating voices and instruments, but the ACA amps do a very passable job, just not quite as much "breath" to the performers.  Whether the tube amps are revealing realism or a coloration is an interesting question.  Considering the capacitor coupling, low output - even bridged, and the low damping factor the ACAs still managed to control the Wharfedale Denton speakers quite well, with just some minor loss of bass control.  These amplifiers just make me want to build an Aleph J amplifier that much more - stay tuned!

New Project: The Command 1625 Deuce Tube Amplifier

It's been a few years since I've built a DIY amplifier, so I approached this project with some trepidation. With my new house with no dedicated listening room, I went from a multi-kilobuck system to something considerably more down market. But as always, the itch to get back into tubes was too much for me.

So what to build? I'm an audio cheapskate at heart - not because I don't like spending money - but it just irks me to throw down too much money for output tubes. Even the price of an old EH 300B has risen a lot the past few years. So with that in mind I decided to use the 1625, which is a 12V filament version of the venerable 807. Most available 1625s were made during WW2 and used for fighter plane radio sets. There are still scads of them out there and the prices are cheap. I've also used this output tube with another amp and liked the results. So why not use it again?

And for those keeping track, this is the second time I've built an amplifier using the 1625, so I added Deuce to the Command 1625 name.

I know I wanted some power which gives me greater flexibility when it comes time to replace my B&W Matrix 805 speakers. So I decided to do something different and parallel the two output tubes. Guesstimated power output would be 16-20Ws if I run the 1625 in pentode (ok Tetrode!). So I scoured the web for ideas, checked out different schematics and asked a few questions. And I came up with the following design (no schematic yet):

12HG7 pentode driver, parallel 1625 output tubes into a 2500 ohm Hammond 1627SEA, a real beast of an output transformer. No global feedback around the transformer, instead I decided to experiment with plate-to-plate feedback.

Screens for the input and output tubes are regulated via gas tubes. Raw power supply is a simple CLC filter using a 5AR4, large polypropolene capacitors, and a 6H choke.

Off on switch, gain controls and banana jacks for 4-8-16 ohm speakers. Also current meters to see the health of the output tubes since in the past I've had gassy 1625s that went into runaway.

Once I was done with the design, it was time to start gathering parts and figure out top plate dimensions and where to drill the holes. For a clean, non-DIY look I went with Front Panel Express.

Soldering everything together was a matter of patience - and my usual sloppy spaghetti point-to-point wiring. I would only devote an hour or two a day to minimize mistakes. I also ran into some fitment issues that required some uh, judicious modifications.

The first time I turned the amplifier on, I was a nervous wreck. As I said it had been a few years since I built anything. Was I going to get a ton of hum? Distortion? Some problem I couldn't track down? Or worse, a whole bunch of smoke?

Well there was no smoke but I did get some hum and a lot of distortion. And so began some very frustrating troubleshooting. Long story short, plate cap tubes made for radio transmitting like to make a lot of RF. Two tubes in parallel only compounded the issue. I'm no expert HAM radio guy, but the differences between the two output tubes may have caused a tank circuit, or something weird like that. Luckily there was a solution - add carbon composition anode stoppers to the output tubes. Since these are plate cap tubes the resistor and small hand-wound coil will have to be added to the lead. Once I did this the distortion and hum dropped to the point where they were no longer audible.

Now I have to build another monoblock and make some cleaner plate cap leads since I'm no fan of exposed voltage.

Sound? Since with this amp I can only listen through one speaker I can't say much about soundstaging depth. But using an extra DVD player and a single B&W 805, I heard a very clean 'n' clear presentation with a good top-end and good bass control from the 4-ohm tap. Not very "tubey" warm sounding but more neutral than that

Stay tuned for Part 2. where I build the second monoblock, give a schematic, and do some listening tests.

Building a new Dynaco PAS-3 tube preamplifier

The existing Dynaco PAS preamplifiers are now all getting a little long in the tooth - with a history that goes back to the Golden Age of stereo, this simple circuit has provided many of an hour of audio enjoyment.  Sure there are more transparent and detailed units out there, along with newer products with better reliability.

But I do have many fond memories of the Dynaco PAS - the first time I heard Quad ESL-63s, and with surprising results coupled with a simple Mosfet amplifier from Stereo Cost Cutters driving a pair of Wharfedale Diamond V speakers.  Both had huge soundstages - both in depth and width - along with a thoroughly musical presentation.  In an effort to capture those glory days, I decided to give this preamplifier another whirl, but this time decided I wanted to build it from scratch.

Chassis and many of the parts from Dynakits.com, while everything else was from various Ebay sellers, along with a few stops at Mouser.

For now this will just be a picture presentation.  Updates later.

Tube Review: The Mullard XF2 EL34 pentode

Introduction:
The Mullard EL34 - though perhaps not the best sounding of this family of tubes - is famous for a big and rich sound favored by guitarists and hi-fi nuts.  The XF2 version, like many early tubes, has welded plates, along with that thick, dark getter that is a trademark of the valves that rolled out from the Blackburn factory.  Later ones have similar construction but used crimped plates - I've never sat down and compared the different XF models, but needless to say they're all pretty good.

 The Mullard "sound", for whatever reason, has always been on the darker scale than neutrality.  Perhaps there is some secret mojo in the cathode chemistry or the metal quality, but this sound difference is easily noticeable in comparison to an original Philips EL34 or even any modern EL34.  This romantic sound, in the wrong amplifier, can lead to a syrupy sound - I'm thinking of something like a stock Dynaco 70 or any vintage amplifier with weak power supply capacitors and/or oil coupling capacitors.  So, like anything else, system balance is important.

The pair of Mullard XF2 EL34s I'm reviewing here are high mileage units pulled from my Eico HF-60 monoblocks.  Though they have plenty of hours on them, they still test almost as new - longevity is something that vintage tubes seem to do well and is needed, especially when running in something as abusive as the HF-60.  For this amplifier with a plate voltage of 400VDC and a screen of 250VDC, 60mA was chosen as a nice cruising speed.

Listening Tests:
The Immortal Otis Redding has a nice and punchy sound, albeit a tad stripped down.  The Mullards conveyed this simple recording with excellent clarity, depth, and dynamics.  Otis's voice sounded very natural as did the instrumentation.  The sound never became harsh or strident with this output tube.  There was also a nice projection to the vocals, pushing the sound beyond the speakers.  This seems to be a trait of vintage tubes - an enveloping sound with a 3-D effect: layered depth, wide and stable imaging, and a sense of being tangibly involved in the music.

Frank Sinatra - Sinatra at the Sands appears to be a three channel recording with instrumentation on the left and right with Frank right in the middle of the action.  The dynamics - on the right system - are truly breathtaking.  The Mullard EL34 excelled here, sounding almost as big as the Tung Sol 6550.  On the quieter songs like Don't Worry 'bout Me, all the emotion came through with the sensitivity that only Sinatra could surprisingly pull from that playboy act.

The last record in this listening test was Steely Dan - Aja which is a modern recording with deep bass, shifting dynamics, and crafty compositions.  The Mullard EL34 wonderfully captured the trailing edges of the reverberation and gave a soundstage that was big and organic.  The instruments floated nicely in space too.  There was a touch of darkness to the music, giving a not quite neutral sound compared to a Tung Sol 6550 or the ultra-vividness of the Philips metal base.

Conclusion:
The Mullard EL34, compared to the new production tubes I've heard, has a real magic.  The music flows with more ease - a naturalness that is hard to describe, but the sound that is reproduced is cut from the same cloth in a grain-free way that makes me forget that I'm listening to a stereo.  Even the Shuguang GEKT88 - which is very good - doesn't capture this ability of convey the real soul of the recording.

However, the Mullard is not the most hyper-detailed and bends the signal to a darker, more romantic spectrum.  But this is a nice place to be - especially in the world of hot digital recordings and aggressive moving-coils.  If you're searching for the most transparent or an abundance of detail, then this may not be the tube for you.  But - and this varies from listener to listener - any sins are easy to forgive.  This is a tube for the music lover, not the nitpicker. 

Tube Review: The Shuguang EL34B pentode

Introduction:
Ah - the legendary EL34 pentode which has been the heart and soul for classic guitar rigs and my first ever tube amplifier, the Dynaco 70.  Developed (with several ancestors) by Philips for PA use, this slim bottle cannot be mistaken for any other tube out there.  Lately this tube - at least in some quarters - has gotten a bad rap as being too warm or not a real audiophile contender, unlike the 6550/KT88 or even (ha!) the 6L6 family.  I strongly disagree with this, thinking the EL34 is one of the most musical tubes out there, walking a fine line between a triode romance and warmth, and the more dynamic sound of the 6550.

The Shuguang "B" version of the EL34 is the stock tube in countless amplifiers and has been labeled Ruby, Valve Art, and who know what else.  It's quite common for new owners to ditch these tubes for something more upscale from the Russians, like the EH, Tung Sol or Genalex "re-issues", or even something NOS like Siemens or Mullards.

There is also the conception that Chinese tubes are prone to blowing up - perhaps a leftover memory from the days of the Jadis JA200 when the Golden Dragon KT88s were referred to as firecrackers.  At least with my experience using the EL34B tube, I've put the hurt on them with the Eico HF-60 monoblocks.  Each tube was consistently taking 500VDC on the plate at 60mA.  That's right on the edge of max dissipation but I never had one blow up.  I'm not sure what modern tube I would trust to take that kind of abuse.

Just for fun, replaced the GEKT88's in the Multi-Valve amplifier with a pair of used and abused Shuguang EL34s from my junk box.  I set the bias point at 60mA which seemed to be the sweet spot.

Listening Test:
For amplifier warmup I listened to my very rare copy of These Immortal Souls - Get Lost (Don't Lie) which has big heavy drums and the chilling guitar work of the ex-Birthday Party member Rowland S. Howard.  The sound is naturally dark and dirgey - this is no audiophile recording - but still incredibly enjoyable.  The bass was big with tons of impact and slam while the midrange had a nice tube "glow" that added to the musical experience.  The treble did, however, seem a tad rolled-off which may or may not be a good thing depending on your speakers.

Neil Young - Live at Massey Hall is a great sounding record.  With the EL34Bs in place I heard plenty of warmth - a bit excessive - that could be a rough analog of the classic Mullard sound.  Where the Mullard still manages to have good detail, the Shuguang lacked in this department.  It wasn't actively annoying - more a sin of omission - but just don't expect to hear everything on the recording.  Nonetheless, Neil Young's voice and guitar work were very natural sounding.  It was the hall reflection and some of the minor audience sound that went missing.

For something more dynamic, I tried out Classic Records re-issue of The Who - Tommy.  The bass and dynamics were very good, but the darkness/warmth was enough to cloud the instrument shimmer, resulting in a less exciting sound.  Depth and instrument placement weren't bad, but nothing close to a vintage Tung Sol 6550 where the images float beyond the boundary of the speakers.  Instead you are left with a closed experience - reminding me of a stock Dynaco 70 that needs to be re-tubed and re-capped - still pleasant but not the ultimate in fidelity.

Conclusion:
The Shuguang EL34B makes no pretenses of being state of the art, but it is a good working man's tube - and being available at ridiculously low prices can be used and abused without too much concern.  These obviously don't have the greatest cathode or metallurgy so tube life on these isn't the longest either.  However if you have an old Dynaco 70 laying around or need to retube a friend's Marshall, the Shuguang EL34B is not a bad choice.  I certainly prefer its presentation over that of the Electro-Harmonix (thin bottle) EL34 which, in comparison, sounds like a bad solid-state amplifier.  As always, YMMV.

Review System:
VPI Aries with JMW 10.5i tonearm and SDS Power Supply
Dynavector 10X5
Cardas Cross 1M interconnects
Quicksilver preamplifier with Mullard short-plate 12AX7s, RCA 12FQ7s, Amperex 12AU7
Cardas Quadlink 5C 1M interconnects
Multi-Valve Stereo amplifier
Cardas Hexlink speaker cable
UREI 813A monitor speakers
VTI BL503 equipment rack 

Tube Review: The Shuguang GEKT88 tetrode

Introduction:
The KT88 was GEC's answer to Tung Sol's big dog 6550, the most powerful consumer output tube at the time.  The '88 boasted even higher plate and screen voltages, the latter an important consideration for Ultralinear output stages.  The KT88 was used in some of the more powerful amplifiers of the time - the Dynaco Mark III, the Harman-Kardon Citation II, the Scott LK-150 - back when 50 or 60Ws was considered an insane amount of power for driving your efficient horn speakers.

Of course times goes on and new technology comes along - instead of a 60lb amplifier with massive output transformers and making enough heat to fry an egg, the consumer can get a cool running amplifier for way less money and in a considerably lighter package.  But even then there are a cohort of audiophiles who won't give up valves since they have an interest in a colorful and lively presentation when listening to their music.

The GEKT88 - also sold as a Penta KT88SC - is rumored to be Shuguangs direct copy of the now incredibly expensive GEC original.  I don't have an original on hand - this was a tube that I never had much interaction with even in the early 90s - so I can only compare by images.  Hmm... solid-plate, getters on the side, similar mica location... bulb structure is slightly different.  The rumor is that Shuguang is using the actual GEC machinery and some ancient batch of cathode emulsion.  Perhaps that's true, but how do they sound?  There was only one way to find out: I ordered a pair via Ebay and waited four weeks for them to arrive from China.

After some time in the Multi-Valve amplifier, dialed in at 70mA each, it was time to do some serious listening.

Listening Tests:
Since Neil Young - Live at the Cellar Door is one of the newest entries to my record collection, I decided to give this the first spin.  The GEKT88 proved itself right from the get go with a big clear sound with plenty of body in the guitar and piano.  The vocals are right in the middle of the speakers and project out much like the real thing.  The coughs and wheezes of the audience weren't lost in any background smear nor did they stick out in an unnatural way with some false heightened detail.  On the song Expecting to Fly, Neil really pounds those piano keys and all that power comes through in a natural way.  So far I'm quite impressed, but this is an album without bass or drums, so I thought it was time to move on to something even more dynamic.

My UK pressing of Supertramp - Crime of the Century is not as bold sounding as my U.S. one, but is a tad smoother.  With the GEKT88s in place, the bass went down real deep with plenty of impact.  Image depth was about real close to the best NOS stuff I've heard while side-to-side soundstaging was excellent.  What this new production tube seems to lack is just that last bit of true greatness I hear with vintage Tung Sol 6550s or Dutch Philips EL34s.  It's very close, but there is some faint but audible grain in the upper mids.

Fleetwood Mac - self-titled was up next.  The vocals were nice and smooth and the multi-tracking of the drums was very obvious.  Though this is a "busy" recording, it is still easy to pick out individual instruments in the mix.  Stevie Nick's voice was sublime with some real emotion coming through.  Very nice.

My promo copy of Earth, Wind & Fire - All 'N All is a hot - and I mean aggressive - recording - with plenty of top-end.  This came through with out any rolled-off treble or excessive tube "warmth"..  The bass and the thwack of the drum started and stopped without any overhang.  It was also easy to pick out different vocalists in the chorus.  A fun and engaging album, the sound came through with great clarity.  I've heard this album done better - like through the Eico HF-60s with their seemingly unlimited power - but the GEKT88s in the Multi-Valve amp were a close runner-up.

Conclusion:
As far as new production power tubes go, the GEKT88 is the best I've heard - so far.  Of course there will be other reviews coming up, so stay tuned.  Needless to say this Shuguang power tube really captures 90% of the magic of NOS, only failing at the very edges that still makes me prefer the vintage stuff.  Of course I am talking about that last bit of inner detail, liveliness, and that sense of being totally immersed in the stereo experience.  Nonetheless I give these tubes a high recommendation.


Review System:
VPI Aries with JMW 10.5i tonearm and SDS Power Supply
Dynavector 10X5
Cardas Cross 1M interconnects
Quicksilver preamplifier with Mullard short-plate 12AX7s, RCA 12FQ7s, Amperex 12AU7
Cardas Quadlink 5C 1M interconnects
Multi-Valve Stereo amplifier
Cardas Hexlink speaker cable
UREI 813A monitor speakers
VTI BL503 equipment rack  

Tube Review: The Reflektor 6P3S-E power tetrode and the Sovtek 5881

Introduction:
Way back in my college days, I used to own a Harman-Kardon Citation V amplifier, which was supposed to use 7581 output tubes.  At the time those were rarer than GEC KT66s, so I ended up running RCA black-plate 6L6GCs which had the misfortune of being on the edge of their max dissipation.  A red line would appear right along the plate seam, at the time making me nervous as hell.  The only inexpensive tube that could take the heat was the newly introduced Sovtek 5881.  It wasn't the best sounding tube but it certainly could take the abuse.

The 1970s era 6P3S-E - except for the shinier getter - looks exactly the Sovtek 5881, but the former has become a sort of budget audiophile darling while the latter is known as a rugged guitar tube.  I was curious to see how the 6P3S-E would sound, and at roughly $24 shipped for a pair, I thought it was a perfect tube to try out in the Multi-Valve amplifier which had adjustable fixed bias - needed for dialing in a larger number of popular octal power valves.

Since I also have a pair of newer 5881s on hand, I also decided to compare the two.  Physically they appear to be the same tube - rather business-like - but perhaps the cathode chemistry or even the plate metal quality is different enough to make a real world difference.  Let's find out!

Note: 6P3S-Es were burned in for approximately fifty hours before listening.  The Sovtek 5881s have been used for regulator service and for testing new amplifiers - hours are unknown but definitely more than a hundred.

Listening to the 6P3S-E:
Blue Nile - Hats is a rare vinyl treat with swooping synthesizers and melancholy lyrics.  It isn't the most natural sounding album but has great dynamics and a dramatic soundstage.  Through the 6P3S-E, there seemed to be a touch of iciness - perhaps an artifact of the recording - but I've heard more richness with other output tubes, notably many NOS units like the Mullard EL34 or the Tung Sol 6550.  But still, the 63PS-E has a good transparency which will be loved by many modern music listeners who grew up with solid-state gear.

Next up was the half-speed master of Willie Nelson - Stardust.  Detail was very good, though not the best I heard.  It was the kind of fake detail caused by excessive treble.  Once again I was reminded of a good, but slightly aggressive solid-state amplifier.  Perhaps this tube would be a better match with some paper tweeters or a dull front end, but with a horn tweeter and a moving-coil cartridge the sound was rather forward.  Bass depth and control, however, was quite good as was transparency.  I wish I could combine the 6P3S-E with the darker sound of a Mullard XF2 EL34.  That would give a more ideal tube.

I dug out my copy of Steely Dan - Pretzel Logic and gave it a spin.  The treble energy didn't seem as hot on this album, but once again I heard a slight sterility to the sound.  It wasn't bad - but the 6P3S-E seemed to falsely increase detail by cranking up the treble, adding some glassiness.  The sound didn't really breathe at least not with the musicality I expect from the very best of the NOS tubes.  I didn't get carried away with the music either, not even the soaring vocals of the song Barrytown.

Listening to the Sovtek 5881:
After some warmup I started with side two of The Grateful Dead - Terrapin Station, which is a very unique "rock opera" type piece.  Once again the forward nature of this tube was evident.  I'm thinking if I had an A/B switch box I wouldn't be able to tell the difference between this and the 6P3S-E.  It had the same tipped up top-end, clean mids and good bass control.

In the right system, Cat Power - Jukebox has a big "you are there" sound.  With the 5881, the effect was lessened, losing some of the inner-detail and the lowest, full bass.  Again, it was good but the big DEPTH was shortened, making a flatter, less involving soundstage without the shimmer and swirl of the best output tubes.  If there were differences between this and the 6P3S-E, they were incredibly minor.  Just to be sure, it was time to return to a record I have already listened to.

Once again I gave Willie Nelson - Stardust a listen.  Perhaps it was listener fatigue or system break-in, but I would swear the treble was actually tamer than the 6P3S-E.  The mids were also a tad richer too.  Both tubes, however, were still cut from the same sonic cloth - perhaps the difference between a Mullard XF2 and a XF3: different but not extremely so.

Conclusion:
The 63PS-E or Sovtek 5881 aren't bad tubes, but they aren't great tubes.  They certainly aren't very neutral, hewing to a brighter sound than I like.  They have a forward "in your face" sort of character that may be a better match for vintage speakers or certain MM cartridges.  At least in my system, I wouldn't use them - not while I'm running compression driver/horn tweeters and a moving-coil cartridge.  They are, however, recommended for budget audiophiles, but with serious system matching caveats.  As always, YMMV.


Review System:
VPI Aries with JMW 10.5i tonearm and SDS Power Supply
Dynavector 10X5
Cardas Cross 1M interconnects
Quicksilver preamplifier with Mullard short-plate 12AX7s, RCA 12FQ7s, Amperex 12AU7
Cardas Quadlink 5C 1M interconnects
Multi-Valve Stereo amplifier
Cardas Hexlink speaker cable
UREI 813A monitor speakers
VTI BL503 equipment rack 

Tube Review: The Valve Art 350B pentode

Introduction:
The original Western Electric 350B - which I've only heard in a few rare instances - has become one very expensive output tube.  Valve Art, through Shuguang, currently makes a "reproduction" that is extremely affordable and has a nice vintage "G" bulb shape that would look quite good in a pair of Quad II monoblocks or any other vintage amplifier that can handle the extra filament current of the 350B over the more pedestrian 6L6GC.

I purchased a pair of Valve Art 350B from Antique Electronic Supply.  Price is less than $40 a pair, which is quite inexpensive compared to the majority of NOS and even new tubes.  Construction quality is quite high with  welded plates, good looking mica, two vertical support rods, and white ceramic spacers.  No, it isn't anything like a 1940s 807, but it looks pretty close - perhaps if you rubbed off the Valve Art logo it could fool some of your more tube savvy friends... or not.

I plugged the 350Bs into my Multi-Valve amplifier which has adjustable fixed bias.  I dialed them in at a healthy 60mA, perhaps 50mA would be a safer bet for long life, but at this price I'm willing to give up a little longevity for a few (and I mean a very few) extra watts.  After all, I'm not running horn tweeters in a multi-amp system, but a pair of full-range speakers that can take whatever I can dish out.  At this bias setting there was no sign or red plating and the tubes have been working perfectly after a good solid 100 hours or more.  So much for the myth of poor Chinese tube reliability. 

Listening:
The first record up was Neil Young - Live At The Cellar Door.  Detail - audience coughs and  hall ambiance were all there - perhaps lacking compared to the best NOS I've heard, notably the Philips metal base EL34s and vintage Tung Sol 6550s.  However no frequency aberration stuck out and there didn't seem to be any of the "solid state in a bottle" bleaching that is often the hallmark of new production tubes.  This recording, however, is not the most dynamic so it was time to move on to something else.

My Japanese pressing of The Police - Synchronicity is an exciting and bouncy album requiring plenty of power to unravel everything that is going on.  With the Valve Art 350Bs, I noticed that the bass didn't go as low as the vintage Tung Sol 6550s.  The 350B sounded compressed and confused on the big peaks - perhaps hitting the edge of their power envelope in this single-ended amplifier.   A more efficient speaker could perhaps ameliorate this issue.  I also noticed a touch of dryness - though maybe this is a function of the recording itself.

Pink Floyd - Animals is a perennial favorite of mine - my German pressing is very dynamic with tons of detail.  With the Valve Art 350B, I noticed a murkiness to the sound as if a layer of gauze was making the finer detail and attack of the songs.  Sure, the music was still there, but I found my mind wandering.  The "swirl" - as I call it - was missing; this is the moment when the notes become visual, engrossing the mind with music.  Depth also become shorter and the soundstaging less enveloping than normal.

I tried a few other albums - Roxy Music, Dr. John, an Agalloch CD - and found that the quieter cuts fared better.  Once the dynamics cranked up, the bass would become plodding and the music unrefined, bringing down the system sound quality down several notches - turning my pride and joy into a sonic mess.  Adjusting the current down to 50mA didn't seem to make any difference either.

Conclusion:
I really, really wanted to like these tubes.  I mean they look great and I'm usually a champion of Chinese tubes, but - at least with this amplifier - I cannot recommend the Valve Art 350B.  Perhaps in push-pull or with a different transformer load, voltage, or current, or even cathode bias they would shine.  Or maybe I was asking too much out of them, but the SED 6L6GC in the same circuit sounded much better.


Review System:
VPI Aries with JMW 10.5i tonearm and SDS Power Supply
Dynavector 10X5
Cardas Cross 1M interconnects
Quicksilver preamplifier with Mullard short-plate 12AX7s, RCA 12FQ7s, Amperex 12AU7
Cardas Quadlink 5C 1M interconnects
Multi-Valve Stereo amplifier
Cardas Hexlink speaker cable
UREI 813A monitor speakers
VTI BL503 equipment rack

Project: Mult-Valve: The Universal Pentode Amplifier

Introduction:
It seems like a long time ago, but I remember when the first Sound Practices magazine came out.  For many American audio nuts, the idea of a using an ancient triode like the 300B in single-ended mode was a new revelation.  Of course this was merely revisiting an old technology, spruced up with some modern twists and a hearty dollop of audio hipsterism.  I easily fell into this new movement, making my first ever piece of DIY gear, a 71A linestage using dual-mono mil-spec potted transformers, gas tube regulation, and some vintage oil caps on the output.  After that, it was a series of amplifiers, including PP 6B4Gs and single-ended 2A3s.  All this on a college student budget.  Once I had a real job, I built was my first 300B amplifier using Thorsten Loech's SV83 pentode driver.

But after a while, my interest in this triode movement began to wane.  It was a problem of speakers:  Low power amplifiers require efficient drivers and my experience with the lower priced offerings, including vintage coaxes and more modern designs, left me unfulfilled.  My first experience with audiophile gear included the wonderful Quad ESL-63 electrostat speakers, and nothing I bought seemed to meet that detail, speed, and snap that I remembered so fondly.  I did, however, found myself willing to compromise, thoroughly enjoying the UREI 813A loudspeaker, which ideally requires more power than I could get out of a common single-ended triode running at sane voltages.

With the UREIs, the best all-around amplifier I've heard to date are the Eico HF-60s.  It's a classic 1950s ultralinear design, but runs the EL34s in heavy Class A.  There is a dynamic ease and sense of unlimited power with these classic 60W monoblocks.  Of course some modern components, the addition of a choke in the power supply, and a "battery bias" mod on the EF86 really brought these ancient wonders up to a new level.  But a close runner up was the 1625 amplifier I built, another Class A wunderkind that sounds much better than one would expect considering the budget build cost.  I began to wonder if I could make an amplifier that would make enough power to drive the UREIs, provide class A output, and have the ability to roll in multiple types of output tubes.  The concept of Multi-Valve was born!

The Design:
Most single-ended amplifiers use Cathode or self-bias.  This is an easy way for the circuit determine the idling current of an output tube.  But since I wanted to roll in different sorts of valves, I decided to go with fixed bias.  This decision complicated the power supply since an adjustable negative voltage is need to put across the grid of the output tube.  This also changes the requirements of the driver tube since output tubes using fixed bias need a smaller grid leak resistor.  That meant my favorite pentode driver was out of the question.  Instead I went with the 5687 dual triode which is a low mu tube that would work well cascaded.



For the power supply, I was limited by the small size of the chassis I had in mind.  So I went with a a simple CLC filter using a 5AR4 rectifier, a Solen, a Triad Choke, and then a larger motor run polypropolene capacitor.  RC filtering with some nice Panasonic capacitors and wirewound resistors provide the lower voltage for the driver stage.  Filament is all AC, but I referenced it to ground using a pair of 100 ohm resistors.  The bias supply is a standard Dynaco-type half-wave solid-state rectifier and some CRC filtering.  A pair of linear potentiometers provided the necessary adjustment, while current meters let me dial in the current of the output tube.  With Pentode amplifiers, a reduction in distortion can be found by the use of a regulated screen power supply.  To meet this requirement, I went with a pair of VR tubes connected in series.

Parts:
Instead of Edcor output transformers with their single output tap, I went with potted James 6123HS, which have the outputs for 4, 8, and 16 ohm speakers.  They also look really nice.  However, for the power transformer, I went with Edcor, but bought plain steel bell covers to match the rest of the metallic look I was going for.  Except for the octal sockets, all the small tube sockets are NOS.  A motor run cap suitable for 500VDC was selected, along with some small current meters, miniature pots for the bias control, and some Tocos volume controls.

The most difficult part of building a tube amplifier is the metalwork and chassis.  Instead of the common wood sides, I wanted something different.  Searching through Ebay, I managed to find a nice Chinese unit that included a bottom and top plate, holes drilled in the back for speaker binding posts, an IEC connector, and a pair of RCA jacks.  It's about the size of a Dynaco 70, but with the size of the output and power transformers, I knew it was going to be a tight fit.  To make the top panel, I did a lot of measuring and made several different versions using the Front Panel Express software.


Testing:
Once I had everything wired up - and it was a tight fit getting everyting inside that small chassis - it was time for some testing.  I first tested the bias controls, making sure that the maximum voltage was set.  I then plugged in all the tubes - GE 5687s, Sovtek 5881WXTs, a GE OA2, and a GE OB2 - except for the Shuguang 5AR4.  Leaving the rectifier tube out allowed me to check that I hadn't messed up on the filament wiring.  Once that checked out okay, it was time for the smoke test.  After I plugged in a pair of cheap test speakers and a running CD player, I had the DMM ready to go with the ground lead already attached to a ground point.

Is there anything more exciting than turning on a brand new tube amplifier?  Okay, don't bother to answer that question - of course there is!  But I still get a little rush even though I've been at this still hobby for 24 years now.  To my surprise there was no smoke or flames shooting out the top.  Instead there was a nice purple glow of VR tubes and that warm orange filament color.  After some quick voltage measurements, I adjusted the bias upward and music started flowing out of the little 4" woofer of the Pioneer test speakers.  Ah, it sounds like magic.


Listening:
After some further measurements and some very minor fixes, it was time for some listening.  The Eico HF-60s were unplugged and disconnected from the system.  Up went the Multi-Valve amp and on went the Cardas wiring.  I replaced the Sovtek 5881s with a pair of vintage Tungsol 6550s which required a bias change.  I started with a Schiller CD on the Sony player, adjusting the gain knobs until I found a suitable match with the Quicksilver preamplifier.  After I was happy with that, it was time to spin some vinyl.  I started with some Tom Waits, checked out some Willie Nelson, and ended up with some Police.  Initial impressions was an amplifier that sounded a little lean, but had plenty of detail, very good bass control, and a suprising amount of dynamics for such a relatively low-powered amplifier.  There was a real 3-D sound with the vocals projected in front of the speakers.  A good beginning...

Of course this amplifier was still incredibly fresh.  Except for the tubes, all the parts were brand new.  So over the course of the next few nights, I used this amplifier to provide background music as I worked out, played video games, or started to brew another batch of beer.  As the hours went on, the lean sound began to recede and was instead replaced by something quite neutral.  I also tried different pair of output tubes that I had lying around - Mullard and Shuguang EL34s.  Both provided very pleasing results, but the vintage Tungsol 6550s seemed to sound the best.


No More Games!
Now it was time for some serious listening.  For this, I invited my fellow local audiophile friend over.  He has a great stash of quality records and also had some different vintage output tubes to try out.  I also replaced the rectifier with a 5AR4 made by Mullard.  Here are some notes from this session:

The first pair of output tubes was a pair of vintage Mullard XF2 EL34s.  Listening to Neil Young - Live at Massey Hall, the darkness and classic warmth of this venerable pentode was obvious.  There was a slight loss of detail, but the overall effect was quite musical.  Some of the macro dynamics seemed a touch restrained.

Next up was the Tungsol 6550.  This pair was from the early 1960s with the grey plates with three holes.  Dynamics really improved here with tight and well-defined bass.  There was also a sense of ease to the music, making the amplifier sound much more powerful than the estimated 15Ws.  Treble detail and extension wasn't the best I've ever heard, but it was still very good, but perhaps lacking that last bit of shimmer and liveliness.  Robert Ludwig's mastering of The Band - s/t album was the best I've ever heard it, managing to find clarity in this darkly recorded album.  On the other hand, Donald Fagan - The Nightfly still had speed and the latent fingerprint of a digital recording.

For the next record, a pair of 1950s Dutch Philips EL34s was selected.  These metal base tubes are quite expensive these days, but there was some real magic here.  Listening to Cat Power - Jukebox was an amazing experience, pulling me into the music in a way that made it seem real and alive; as if I were sitting thirty or forty feet away from the band in a small hall.  There was an evenness to the music from the top to the bottom without any  part of the frequency spectrum sticking out in an unnatural way.  Dimensionality and soundstaging was some of the best I've ever heard.  Even more surprising was the controlled but taut bass through the 15" Eminence woofer.  Very impressive.  These tubes appear to be made for this amplifier.

The following experiment was not much of a success.  A fresh pair of early 1950s Tungsol 6AR6s was selected, along with an octal socket adapter.  The sound on Steely Dan - Greatest Hits and The Who - Tommy, became very uninvolving and flat.  Perhaps some more break-in time was needed or a different bias point.  It was time to move on and try something different.

1970s Gold Lion KT77s (with black bases):  These sounded much like the Tungsol 6550s with excellent bass control and incredible dynamic range.  It was, however, a little richer, hewing somewhere between the dynamic Tungsol 6550 sound and the classic richness of the EL34.  Neil Young - Tonight's The Night delivered all the tortured darkness that I expected with a sense of realism that was inviting.

For a more budget choice, I also tried a pair of SED 6L6GCs, one of my favorite modern production tubes.  Though there was a slight loss of the last bit of detail, the overall sound was very pleasant with only some slight overlaid grain over the music.  The explosive dynamics on Blue Nile - A Walk Across the Rooftops were really a surprise, while the Police - Synchronicity kept the rhythm and pace of the music together in a bouncy and engaging way.


The Scorecard:
Bass: Normally a weakness of tube amps, and even more so for single-ended, the Multi-Valve was a real surprise here.  The lowest notes were deep, well-damped, and had excellent control without the slight tubbiness I normally associate with tube amplifiers.  This is a testament to the James output transformer and the feedback loop controlling the woofer.  Not only was there depth, but detail, whether it was the smack of a tom-tom, or the playfulness of a skilled bass player.

Midrange: Clear, defined, and transparent are the first words that come to mind.  The music is served in an even-handed fashion without tube bloat or an overly analytical presentation.  The quality here is quite dependent on the output tube used, ranging on the scale from amazing (Tungsol 6550s and Philips EL34s) to a more middling sound (Mullard EL34s or SED 6L6GCs).  But at no time, except for the 6AR6s, was I actively disappointed by the music coming out of the speakers.

Treble: This again was dependent on the output tube selected for use, with varying levels of quality.  I preferred the Philips EL34s and the Gold Lion KT77s here, while some listeners, depending on the speakers used, may prefer the warmth of the Mullard XF2 or the qualities of the Tungsol 6550s.  At its best, the Multi-Valve amplifier treble is perfectly integrated into the midrange, not calling attention to itself, but not lacking in detail or extension.

Soundstaging: Whoah!  Images are way beyond the edges of the speaker, making my listening space sound larger than it is.  There is also an incredible amount of depth.  Vocals are also projected forward in a nice fashion, keeping separate from the rest of the music.  This clarity comes from the lack of sonic mud, allowing the listener to "see" deep into the musical performance.

Intangibles: Considering the limited power that single-ended can deliver, one of the biggest revelations was the handling of macrodynamics.  Even at lively listening levels the amplifier never failed to deliver the wattage when needed.  This, along with the various microdetails and instrument shadings, gave a unique presentation that makes so many other tube and solid-state amplifiers sound cloudy or unfocused.  The Multi-Valve isn't stubbornly analytical either, bleaching out warmth or lacking humanity.  Instead the presentation is incredibly balanced.  An amplifier like this would be a great tool for mastering or component evaluation.


Conclusion:
There really is something special about single-ended designs, whether they are triode, ultralinear, pentode, or even solid-state.  It's the Class A power that really matters in the end, along with the uncomplicated driver circuits and simplified power-supply requirements.  A pentode, at least with regulated screens and negative feedback, gives a different presentation than, for example, the classic WE91 300B design.  Of course listening preferences, speaker selection, and source components will greatly effect the best amplifier to use in a given system, but with mine, the Multi-Valve is perhaps the best I've ever heard.  Really.  It's also great fun to sample different output tubes and the unexpected differences between them.  Highly recommended.

Parts list and Front Panel Express layout available upon request.


Review System:
VPI Aries with JMW 10.5i tonearm and SDS Power Supply
Dynavector 10X5
Cardas Cross 1M interconnects
Quicksilver preamplifier with Mullard short-plate 12AX7s, RCA 12FQ7s, Amperex 12AU7
Cardas Quadlink 5C 1M interconnects
EICO HF-60 monoblocks with Mullard XF2 EL34s & 5AR4s, GEC CV4085s, and GE 6SN7GTAs.
Cardas Hexlink speaker cable
UREI 813A monitor speakers
VTI BL503 equipment rack