Snell Type JIII Finale - Sensitive Enough?

With the foam issue out of the way, it's time to wrap this up!

If I never allowed myself to be conned by the Junkyard Jukebox guy to subscribe to his Sound Practices audio rag in the early 90s, I may have soldiered on tweaking my classic push-pull EL84 and EL34 amps and upgrading my LS3/5As (or adding) to this pair of Snell Type JIIIs (or maybe even Type Es) in my listening room.

But things didn't turn out that way...

Altec 755C + Open Baffle + Simple 45 amp

I succumbed to the temptation of single ended triodes + Altecs!

 

In my reality check article, I used the above chart to associate frequencies with the vocal range of humans and acoustic musical instruments. Please use it as a guide to the RTA traces and discussion of frequency ranges below.

Lou Donaldson on Snell Type JIIIs

The Snell Types E, J, and K have developed a reputation as single ended triode (SET) amp-friendly speakers. Arguably, my pair of Type JIIIs can be a good stop gap but I'll try to explain in the simplest terms as to why, in the final analysis, they don't meet my criteria for flea power amplifiers designed with "it's the first watt that counts" ideology.

Snell Type JIII specs

Since I couldn't find a late 80s to early 90s Vifa catalog, I based all the specs from the above information provided by Snell. The low(ish) nominal impedance (Z) of 6 ohms is an advantage when driven by current source devices such as solid-state amplifiers, which can typically supply more power to a lower Z load. OTOH, vacuum tubes are inherently high impedance/voltage source devices, thus requiring output transformers to drive lower Z loads. However, any well-designed tube amp with an 8 ohm tap from the secondary of the output transformer shouldn't have problems driving the Type JIII.

Snell Type JIII

While the man cave is hardly anechoic, this RTA trace is smoother compared to anything I've taken from any of my Altecs. It pretty much tracks the manufacturer's specs.

Altec 753C

In spite of the fact that the Altec 753C's RTA isn't quite as smooth, it has a half octave greater extension in the low end. The top end also starts to roll off earlier, at around 13kHz. But as further discussed below, the performance of the Altec 802D compression driver + Altec 32C belies its 40s Western Electric roots.

Altec 414A vs. Vifa M21

The radiating area of the Altec 414A cone at 95 square inches is 2.5 times greater than the 8" Vifa M21's 38.5 square inches. Both use paper cones - the Altec cone is left bare and suspended by a treated accordion surround, while the Vifa uses high compliance foam and its cone is treated with some form of damping compound. The added cone mass from damping helps low frequency extension. Regrettably, it also reduces speaker sensitivity, among other things.

Altec 414A in wide range mode

In wide range mode, the 414A's 95 square inches of radiating area covers a frequency range of six and a half octaves, starting from around 40Hz-3500Hz. That's just a few notes shy of a piano's range at both extremes as well as the fundamental notes of most acoustic musical instruments and easily, the entire human vocal range. This driver sounds very natural to my ears and plays smoothly with no detectable glare or shout manifested when listening to music. I’m happy to report the tiny spike before 1kHz isn't audible to me. 😉

The Vifa M21's smaller radiating area of 38.5 square inches tasked to reproduce five and a half octaves from 49Hz all the way to its 2700Hz roll off point is a greater challenge.

Altec 414A specs

The 414A goes lower than the Snell JIII but not quite solid down to the claimed 30Hz rated fundamental. With a 99dB/1W/4ft sensitivity, it has an 8dB advantage over the Snell Type JIII's 1.6 cubic foot (cf) ported box rating of 91dB/1W/1M. Housed in a 4 cf bass reflex cabinet, the 414A can definitely move a whole lot more air with minimal power input. 

Reverse engineered Snell JIII crossover

The type JIII's crossover is a bit more complicated than my Altec 753C XO below. Encircled in red is a paralleled choke/resistor/capacitor EQ network for the Vifa woofer. This shapes and/or controls cone resonance in the midrange. Unfortunately, the EQ network also absorbs power.

Case in point, BBC engineers' extensive use of EQ in the LS3/5A crossover made it notoriously inefficient. But to their credit, whether it was the earlier 15 ohm or later 11 ohm version, it was a friendly load, especially to tube amplifiers.  

Altec 753C crossover

Since the 414A has no serious peaks or dips, which I verified through years of listening and later confirmed via RTA, I chose to run it in wide range mode in which the woofer rolls off mechanically. This preserves the efficiency/sensitivity of the woofer and makes the crossover simpler since it only involves a 4 uf capacitor acting as a high pass filter. By using non-inductive resistors, the Altec 802D compression driver is attenuated to match the 414A's sensitivity. Then I adapted the high frequency EQ circuit from the Altec 30923 to tweak the shape of its top end response. 

Left: Altec 802D + 20275
Right: Snell/Vifa D26

For the higher frequencies, Snell chose the Vifa D26 1.25" soft dome fabric diaphragm that has a radiating area of 1.23 square inches vs. the Altec's 2.25" diameter aluminum diaphragm with an equivalent 4 square inches of radiating area. 

Snell employed a sharper 12dB/octave slope high pass filter for the dome tweeter to cut in @ 2700Hz while I blended the 802D compression driver/32C horn combo at a gentler 6dB/octave slope @ 3500Hz in the Altec 753C just where the 414A top end response starts to taper off. 

Altec 802 + 32C horn

My old school high frequency horn loaded system uses the Altec 802D compression driver in conjunction with the 90° H x 60° V dispersion Altec 32C horn originally designed by Western Electric for their 753C monitor system. It's merely coasting along from 3500 Hz, generating the top most octaves and harmonic overtones compared to the hard-at-work direct radiating Vifa dome tweeter diaphragm of 1.23 square inches struggling to replicate the final octave of top end fundamentals from 2700Hz. Hence, the Altec horn system reproduces much faster and cleaner transients with ease, while also enhancing the already effortless presentation of micro and macro dynamics of the high efficiency 414A woofer.

I'm not set up to plot a reactance chart for the Altec 753C and Snell Type JIII but after using them with various amps in my collection, I guesstimate that both proffer a benign resistive load. However, the 16 ohm nominal impedance, simpler crossover of the Altec 753C and its greater efficiency are a godsend to low damping factor single ended directly heated triode amps.

Lou Donaldson on Altec 753Cs

How far has speaker design progressed?

Vifa M21WN-07-04 + Altec 755C

Ever since I built my first pair of open baffles, evaluating drivers in wide range mode in order to gauge their ability to reproduce an accurate midrange has become routine. Listening to the Vifa M21 woofer in this manner wasn't a very pleasant experience because it sounded very dull. This is in stark contrast to the snappier midrange of the Altec 414A, which I've been using in wide range mode for many years. Likewise, the Vifa 8" was totally outclassed by a handful other woofers and wide range drivers in my collection including the 10" Altec 406Z and Altec 756B.

It's a no brainer that the long travel foam suspension + cone damping extended the low frequency response of the 8" Vifa. But to my ears, this was achieved to the detriment of midrange performance. Is bass extension really more important than midrange accuracy in the high-end audio era? Why is cone damping so prevalent in modern drivers? Western Electric, Jensen, Altec, and their contemporaries all used bare cones.

During the era of Western Electric and Altec, engineers used their ears, guided by cutting edge technology test equipment. This can be gleaned from contemporary ads and press releases. I can't help but wonder if the Vifa woofer was designed merely to satisfy test instrument requirements and laboratory standards without any ear testing involved. If that is the case, is that what we consider progress?

I chose the Altec 755C over the near mythical Altec 755A for this feature because IMHO, it is a worthy benchmark for an 8" wide range driver that is still quite accessible and affordable in the real world. Based on the above specs, by the time Altec introduced the 755C in the late 50s (or early 60s?), they had conceded to the spec wars triggered by the commercialization of stereophonic equipment. I've listened to the 755C loaded in an OB, 2cf box or the Silbatone cabinet but never heard a solid 40Hz low end, merely well defined harmonics of that fundamental. 

Simple 46 amp  (1250mWpc) > Altec 755C in Silbatone enclosures

Granted the 755C can go a bit lower, subjectively, its low frequency extension isn't significantly greater than the 755A. I'm glad though that Altec was able to retain much of that captivating midrange + dynamics even if it's not quite as realistic as its older Western Electric-designed 755A sibling.

Altec 755C in the Silbatone box

The Silbatone + 755C combo loses about an octave at the frequency extremes vis a vis the Snell JIII but has a 5dB advantage in sensitivity. Despite the spikes and dips in its RTA trace, I much prefer listening to the Silbatone 755Cs. Maybe the dips and spikes = musical?🤔 

Snell JIII = 1.6 cf vs. Silbatone 755C = 1 cf

Whether driven by my SET amps, Dynakit ST35 or Nobsound/JLH 1969 clone, the Snell Type JIII sounded veiled and anemic compared to the Altec 753C and Silbatone 755C. With the Snells, I have to turn up the volume a couple of notches to be engaged musically but with the Altec 753C or Silbatone 755C driven by my weakest 750mW per channel SE71A amp, I already hear subtle details even at background sound pressure levels (SPLs). Understandably, the JIII could not compete with the Altec 753C at the loudest end of the spectrum since it doesn't have the physical size to move as much air. But considering Snell's reputation, I expected better resolution and nuances at low to medium SPLs.

Music Reference RM9 amp > Snell JIIIs

The most convincing full range sound I got from the Snells was when they were driven by the Music Reference RM9 amp, a push-pull parallel/triode connected EL34 stereo amplifier producing 35 watts per channel with the negative feedback set at minimum. Alas, with this combination, the irresistible charm of the single ended directly heated triode amp is lost...I can't have my cake and eat it, too.😔 

Altec 755C in Silbatone cabinet + 3000H super tweeter
Truth be told, lately, I find the use of a super tweeter redundant

Through the years, I’ve tested a few vintage and contemporary 8” wide range speakers but haven't found any which could closely approximate the 755C’s sound quality. The design isn’t rocket science and if Great Plains Audio still has the original tooling, I don’t see any reason why the humble 755C PA speaker can’t be reproduced at a reasonable price. That would be a great boon to single ended directly heated triode amp aficionados, especially those who have limited space in their listening room.😊 

Altec 753C + Snell Type JIII

Contrary to current trends in speaker cabinet design, the wider front baffle area of the Altec 753C cabinet (and to a lesser extent, even the Snell Type JIII), enhances projection by acting as an acoustic soundboard. Western Electric and Altec speaker systems were usually fitted with wings in theater installations, which is the main reason I've been an advocate of the wide open baffle. In principle, this is practically no different to the fully open lid of a grand piano during a performance in a concert hall.

Altec 753C + mini tour of the man cave 

The Snell Type JIIIs can give a glimpse of what directly heated single ended triode amplifiers can do. But these are definitely not end game speaker systems for those who want to indulge in the delights of flea powered single ended directly heated triode amps. As competent as the Snells are and given their already above average sensitivity (compared to typical high end audio speakers), they could never spook me into believing musicians come alive in my man cave the way my Altecs can at times. For some organic reason, I can also listen to my Altecs for extended periods without listening fatigue creeping in. Keep in mind though that the empirical and subjective observations embodied in this article only reflect my musical aesthetics and priorities. YMMV. 

I hope I was able to illustrate that there's no myth or magic to a fine sounding and efficient speaker system. All it takes is a basic understanding of the physics of sound and learning how to compromise.

Go back to Part 1 and Part 2

OJAS @ Lisson Gallery NYC

Our dear friends Charito and Joey, whom we haven't seen for over five years, were in NYC visiting for a couple of days. On short notice, Tish was able to take a day off so we were able to meet up with them. Joey is an avid audio DIYer and was a frequent collaborator especially during the annual November Hifi Show when I was still based in Manila. He represents G.I.P. Laboratory in the Philippines. 

It was also timely that Devon (OJAS) Turnbull's HiFi Dream Listening Room No. 1 exhibit at the Lisson Gallery NYC was on its penultimate week. So Joey and I agreed that this was going to be our meeting place! 

The OJAS loudspeaker system utilizes Great Plains Audio drivers, which are currently produced using original Altec tooling - GPA 416B 16" woofers + GPA 288H 1.4" compression drivers. The latter compression drivers are coupled to bespoke OJAS 1505 horns, which are remastered versions of the classic Altec 1505B multi-cells, while Pioneer PTR9 ribbon super tweeters fill-in the top-end octave harmonic overtones. At the center is a Fostex FW800HS super woofer. Devon starts with Werner Jagusch crossovers but driver loading and alignment are all developed in-house and then fine tuned by ear!

Having spent almost a decade studying at The Juilliard School twenty years before the Diller Scofido + Renfro reboot, I developed an immediate affinity for the brutalist vibe of the speakers!

The OJAS gestalt brought back cherished memories of the late Don Garber's Fi audio gallery from the early 90s, which was along 30 Watts Street in SoHo NYC. I wasn't able to ask Devon if he got the chance to meet Don. I bet they would have gotten along really well!

A pair of Altec/Peerless 4722 SUTs are mounted directly on a FET-based phono preamp using vacuum tubes as constant current sources. This was designed by jazz guitarist Steve Berger, who's also the man behind Aprilsound NYC. The adjacent chassis with two large knobs houses a transformer volume control wound by Dave Slagle of Intact Audio.

Being a devoted Garrard 301 listener for many years, Devon is cognizant of the finite supply of these idler driven classics. So for this project, he chose the platter + motor from a Technics SL1200G and mounted them in a custom layered plywood plinth. To assure absolute speed stability and smoothness in operation, a 3-speed linear power supply was specially designed by Linear Tube Audio. Having done DJ work during his younger years, he admits that his choice was partially in reverence to the marque.

Mounted at the back is an Ortofon RMA309 tonearm + a restored vintage SPU-A for stereo LPs and a Dynavector DV505 tonearm + SPU mono CG 65 Di for 78 rpm shellac discs.

Devon's pair of SE300B mono-blocks (fitted with Tango XE20S output transformers) is an homage - not a slavish copy but his own interpretation - to Herb Reichert's Flesh and Blood amplifier published in Sound Practices Issue 8. 

Unlike a typical hi-fi show swarming with silver-haired or balding guys, it was refreshing to be surrounded by a twenty-to-forty something crowd. Devon is attracting and developing a niche market uncharted by mainstream high-end audio publications such as Stereophile and The Absolute Sound. Due to his background in design and interaction with the upper echelons of the fashion and music industries, the whole Sound Practices ethos of music reproduction spearheaded in the early 1990s by Joe Roberts will hopefully reach a larger audience. 

Joey and I spent a couple of hours listening to Blue Note jazz, contemporary classical music, and talking shop with Devon. He was a very gracious host, who candidly gave credit to his collaborators as well as to those people who've influenced and inspired him.

Me, Devon, and Joey

Bravo, Devon, very well done! 

After several years of PMs, it was great to finally meet you. I look forward to more shop talk when you visit my man cave.

Devon's HiFi Dream Listening Room No. 1 exhibit at the Lisson Gallery in Chelsea NYC is really worth hearing and seeing! 

Open Monday - Friday from 11am - 6pm until August 5, 2022.

This 'zine contains comprehensive information about the whole hifi installation + more! 

The poster + 'zine is available at Printed Matter Inc.

 

Snell Type JIII Part 2: $25 foam vs $40 Euro foam

Re-foaming the 8" woofer found in various incarnations of the Type E, J and K Snell speakers is a very contentious issue exacerbated by their cult-like status amongst audiophile admirers. 

Vifa M21WN-07-04 woofer
Left = $25/pr. foam (yellowish tint), Right = $40/pr. Euro foam

In this day and age of marketing hype, spending $100 or so to import a pair of alleged original foam from European sources is, IMHO, not justifiable. How does one determine which retailer is being truthful?

Given that I wanted to give this project my best shot, when I noticed that Simply Speakers* added a Euro version to their website for $40 a pair/shipped, I placed an order. This is just one of the many reasons why this installment has been delayed. 

*No affiliation, just a satisfied customer!

WARNING!

In Part 1, I re-foamed my pair of Vifa M21WN-07-04 woofers using the $25 foam kit. I specifically mentioned that the dust cap and cone are just one piece. 

I've seen discussions in audio forums suggesting the removal of the dust cap to center the voice coil. I have to reiterate that the removal of the dust cap = a DESTROYED woofer!

After using both these foam kits, I can confirm that the voice coil on this particular Vifa woofer is self-centering. If you encounter voice coil problems, it's either the foam you used is suspect or you seriously deviated from the instructions.

RTA Traces

$25 foam vs. $40 Euro foam

Only one Vifa M21WN-07-04 was fitted with the Euro foam so I could compare them.

Die-hard Snell aficionados and "specialist" retailers contend that "generic foam" will kill the bass response of the Vifa M21 woofer. Given the RTA traces below, which foam is generic?

Snell JIII with Simply Speakers $25 foam

This trace pretty much tracks the original specs at hifiengine.com. 

Snell JIII with Simply Speakers $40 Euro foam

If we split hairs, this $40 Euro foam trace looks just a touch more ragged. 

Euro foam serial number

FWIW, unlike the $25 foam, the Euro foam has a serial number. Does that give it more credibility?

Listening to Foam 

$25 foam vs. $40 Euro foam

Evaluations were conducted in full dimensional mono! 

The sonic dissimilarity was very subtle. It only became obvious in A/B comparisons in which I was consciously listening for a difference. Also, as usual in audio, better metrics don't necessarily = better sound because audio tests (in this case, pink noise) are static while music is very dynamic! 

Listening to Billie, Ella, Julie, Frank, Tony and Johnny H, it was relatively easy to discern better midrange presence from the unit fitted with the Euro foam. When I pulled out my Ray Brown, Curtis Counce, Charlie Haden and Mingus CDs and LPs, I heard more tuneful and articulate bass lines from the Euro foamed woofer. The woofer with the $25 foam had a tendency to sound boomy while the midrange was just a touch veiled. 

That said, if your Vifa M21s are already fitted with the $25 foam replacement and you're not very DIY savvy, it's nothing to lose sleep over. IMHO, you're still listening to a pair of very decent classic speakers. However, if you're a seasoned DIYer restoring an unmolested pair of Type Js or Es with rotten Vifa foams, go for the $40 Euro foam!

 Is the $40 Euro foam the original foam?

The Time Tunnel

I wish I could travel back to the early 90s to find the honest-to-goodness truth.

Instead of worrying about matters beyond my control, I'm going to replace the $25 foam on the other Vifa M21 with Euro foam so I can listen in full dimensional stereo!

Go to Part 3 or back to Part 1

Happy Holidays 2021

 With the blessing of Early Bender of Hifitown.com, I uploaded two articles written in the 1980s for The Absolute Sound by his parents, Walt Bender (1944-2008) and Lennice Werth. 

WE/Altec 755A is in Part I

Olden Golden Components Part I

Berning EA230 is in Part II

Olden Golden Components Part II

I've owned quite a few of the components discussed and still listen to a couple. This is a reflection of the articles' profound influence on my pursuit of the audio hobby. Since I believe that they are as relevant then as they are now, I added them to the JE Labs Arkiv.

2021 Index

January: Looking back to the past for a Better-Sounding Future + 6C8G

February: Happy Birthday Mommy + Happy Birthday Daddy

March: PSE 6SN7 Headphone Amp + Snell Type J III Part 1

April: Lar Retro-resto Shure M65 phono preamp + Marcel Breuer House with an Altec 604C

May: Hi-Fi for the Deck - Simple Triode'd 6F6/6V6 amp + Kutztown Spring Radio Show

June: morrison micro 2A3 reimagined + Thorens TD124 Tips

July: Old Flame - Rogers LS3/5A + 9"-10" Tonearms from Denon, Fidelity Research and Grace

August: Billingham Hadley Pro & Leica II half case + Gray Research HF500 Turntable & 108B tonearm

September: DKL and Exacta mount lenses & Exa camera + Budget SUTs - Sony HA-T10 vs. Shure mic transformers

October: Kutztown Fall Radio Show & Summer Events + Classic Shoe Mount Light Meters 

November: Tube Rolling Fun (and Peril) & adapters + TT Artisan Light Meter

December: JE Labs Man Cave 2021 + Holiday Greetings/2021 Index

As the year comes to a close, I'd like to thank all the visitors, especially those who've contributed to this blog.😊

Wishing everyone a great Holiday Season and all the best in the New Year!

Tube Rolling Fun (and Peril) + Adapters

Tube rolling is a fun aspect of the audio hobby. It only gets tedious when audiophiles start splitting hairs about a VT231, 5692, etc. I draw the line when an audiophool claims, "...my line stage preamp resolves the R train rumble under Carnegie Hall better when I use a 6AS7 in place of the original 6SN7..." 🙄  

Those two tubes may be pin compatible BUT a power transformer 🔥melt-down🔥is imminent since the 6AS7/6080 draws 2.5 amps @ 6.3V. That's over 4 times more filament current drawn by a 6SN7, which only draws 0.6 amps @ 6.3V.

 💣 💣 💣 Rolling tubes is dangerous unless you have a working knowledge of electronics to comprehend tube data/specs. 💣  💣  💣 

It's been a while since I listened through Telefunken 12AX7 smooth plates on an RCA phono. Since I used to graft this circuit on a Dyna PAS preamp, I ordered a pair of 12AU7/12AX7 > 6SN7/6SL7 adapters to relive the experience on my RCA octal preamp.  

Back in the 90s, Steve @ Angela Instruments had a boatload of Raytheon 5755s and shared a sleeve with me. Since I never found a project requiring these tubes, I got a pair of 5755/WE420 > 12AX7 adapters to listen to them in the Shure M65 clone. Piggy-backed to 12AX7>6SL7 adapters, they also worked nicely with the octal phono preamp. 

Despite slight differences in transconductance and plate impedance between the 6SL7/7F7 and their younger 9-pin siblings (ECC83, 12AD7, 5751 and 5755), there was no visible variation in square waves nor frequency response aberration when I bench tested those tubes in both circuits.

Admittedly, loctals don't look as glamorous as their octal cousins with bakelite bases. But I'm very fond of them to the extent that I built and use a full function loctal preamp. I've been adopting unloved loctals at radio shows and hamfests. Essentially the industrial looking 7F7 and 7N7 are rebased 6SL7 and 6SN7, respectively! My only issue with loctals is, the tube pins are prone to corrosion. This is easily remedied by a wire brush + DeoxIT before use.

I purchased these tube adapters from the seller xulingmrs. They are very well made and fairly priced. Shipping cost and transit time from China was also reasonable. Highly recommended!

Budget MC SUTs: Sony HA-T10 vs. Shure Mic Transformers

Way before I knew about SPUs and DL103s, I experimented with an entry level Audio Technica AT31E MC cartridge. Since my NAD 3020 didn't have an MC input, a pair of Sony HA-T10s were recommended at the same discount NYC store. I mounted the cartridge on a Grace G707 which was perched on a "molested" AR-XA. The sound was very different compared to my Grado GTE+1 - quieter background, more detail, deeper and wider soundstage, albeit less midrange presence and warmth.

I moved on to a Grado Signature 8, 8MX, MZ and lost track of my Sony HA-T10s. I probably loaned them to an audio buddy who forgot to return them. During a moment of nostalgia, I hit the BIN button for a pair @ a little over $100, shipped! I've listened to them with all the MC cartridges pictured above and they make pretty nice sounds! 

However, I can only justify the price I paid because of sentimentality. To my ears, the Shure mic transformers below are mucho better performers at ~ $40/pair + some DIY. Remember that HA-T10s were mass produced MC step ups, not limited production transformers using exotic nickel/amorphous/Finemet materials. Thus, sellers asking $200-400/pair are greedy!

 

Through the years, eBay sellers have benefitted from my blurb about Altec 755s, 32 horn, 414 woofer, 4722/15095, GE RPX, Gray Research tonearm + clones, Shure M3D and M7D, etc. Now I doubt if any Sony HA-T10 seller will even link to this upload.😆

Let me just say this to Shure microphone transformer sellers - as good as they are, once you break the $100/pair barrier, you've got tons more competition. So if you've got business smarts, be reasonable!😎

Old Flame - Rogers LS3/5A

As I mentioned in my reply to a reader's query in Snell Type J III, Part 1, I'm the temporary caretaker of a pair of 15 ohm Rogers LS3/5As while my buddy Jose's basement is getting sorted. 

ca. '93

Long time readers know that I was a BBC LS3/5A user. A pair of 15 ohm Rogers replaced my Magnepan SMGas in '86. As a partner in a company that distributed Spendor speakers in the Philippines in the early 90s, I also owned a pair of 11 ohm bi-wireable Spendors. 

ca. '94

In the preceding two pictures, my pair of DIY PP2A3 monoblocks struggled to drive the Spendors in my tiny apartment. Despite that, the BBC near field monitor opened my ears to the virtues of directly heated triodes. Alas, they were superseded by Altec 755s because I needed more efficient speakers to pursue flea-powered single ended directly heated triode (SE DHT) amps.

The Bextrene cone KEF B110  5" woofer + the complex crossover/EQ network = 82 dB/1W/1M, very inefficient! But kudos to BBC engineers, IME, the speaker is still a relatively easy load for low-powered tube amplifiers because of its high(ish) impedance across the audio band. 

Just as I remembered, the LS3/5As are very capable of portraying the midrange magic of an SE300B or even an SE2A3 at near field distances. However, to get some boogie factor out of them, they need the power output of at least a Dyna ST35. But as good as the ST35 amp is, a catch-22 situation ensues because it sounds veiled compared to the aforementioned SE DHT amps.

Snell Type J III + Rogers LS3/5A

I was viewing the past through rose-tinted glasses when I posted (#3) in HiFi Haven - mea culpa! There's a greater similarity in tonal character between the Rogers LS3/5A and Snell Type J III. The Altec sound is another entity altogether!

Given my post SE amp/High Efficiency transducer expectations, the Altec 755As in Dr. Bae/Silbatone cabinets are tonally more lifelike across the audio band, offers better resolution, has more low frequency extension, greater micro and macro dynamics and plays at higher SPLs in a package that's not significantly larger. 

Listening to the LS3/5As was like seeing a former flame. The familiarity is there but the chemistry and fireworks are gone. (◞‸◟)ﾉ