vintage ESS AMT 5 speakers, 1974—Heil AMT's, refoamed 12" Alnico woofers—superb

Description

Offered for your consideration is an exceptional pair of vintage
ESS
AMT 5
speakers, manufactured in Sacramento, CA, 1974.  As you may know, Electrostatic Sound Systems, Inc. was started in 1972 and quickly found audiophile favor with their unique ESS AMT 1 speakers and its use of the
revolutionary
Heil AMT (air motion transformer).  ESS was the sole licensee of the technology and, as such, distinguished themselves from every other speaker company right from the beginning.
The AMT was developed by physicist Oskar Heil and differs from conventional direct radiator transducers, and even planar/ribbon tweeters, with its use of accordion-folded Mylar sandwiched between strips of aluminum.  ESS marketing prose described it some time ago as follows…  “The low mass diaphragm is suspended in a massive magnet structure concentrating an intense magnetic field around the diaphragm.  When a signal passes through the aluminum strips, the bellows-like motion of the folded pleats squeezes air out five times faster than the air motion of a conventional cone driver. The virtual "instant acceleration" provides high definition, crisp transients, and overall spaciousness with superb dynamic range. This type of performance distinguishes the Heil from all other transducers.”
The ESS AMT 5 features a smaller version of the original Heil transformer that radiates forward, not bipolar like the big Heil.  It serves as an upper midrange/tweeter in the AMT 5 as crossed-over from a 12” Alnico magnet mid/bass woofer at a relatively low 1.5kHz.  In contrast with the pyramidal design of the AMT 1, the AMT 5’s feature conventionally-shaped cabinets measuring 24” tall x 14½” wide x 12¾” deep (with grille).  The cabinets are finished in attractive real walnut veneer over sturdy 1” thick MDF and integrate nicely with just about any listening room décor.
So, please have a look at my large photos, the remaining description, and read
Stereo Review
’s 1974 test results on the AMT 5—that I’ve attached at the very bottom of this listing—to decide if these outstanding, hard-to-find ESS speakers should join your collection.
This pair of ESS AMT 5 speakers is in clean, excellent condition.  The walnut veneer is in great shape with no dings or large scratches, just a tiny chip at the rear bottom corner of one that’s practically invisible.  I gave the walnut veneer an application of Formby’s lemon oil since it seemed dry; this should be repeated regularly.  Better yet, a few light coats of tung oil would wake up that grain beautifully (and not evaporate in a short while the way lemon oil does).  But, I think you’ll agree they look very nice as they sit.
Plus, the grilles are also very nicely preserved with no stains, holes, or runs, solid frames, and new aluminum grille emblems.  The grilles attach with an interlocking sphere system that, though more durable than Velcro, is somewhat fussy; once locked, they can be difficult to detach (use a plastic paint scraper to not mar the veneer).  Overall, these remarkable ESS speakers present exceptionally well at all distances!
Background-wise, I purchased these AMT 5 speakers from the original owner, a neighbor of mine who is retiring to Naples, FL.  He told me that the speakers had been sitting in a closet for 25 years, or so, ever since the suspension foam on the woofers had begun to fall apart.  I was so eager to acquire another pair of early ESS—I had some AMT 1B’s ten years ago—that I didn’t even notice a few small differences between the two speakers!
As seen above, the serial numbers are A 133 and A 2080.  So, even though the speakers were purchased as a pair, they were made several weeks, perhaps months apart with A 133 obviously being very early production.  The first thing I noticed was that the early speaker’s woofer has a voice coil center cap that’s smaller than the other, and the adhesive the worker used for the foam surround bled onto the cone edge.  Since I needed to refoam the woofers, I immediately pulled both of them from the cabinets for evaluation.
Based on the lack of an EIA source code stamp on the woofers, only an EIA-format date stamp, “7416”, indicating manufacture in the 16th week of 1974 on one, I believe these woofers were made in-house at ESS.  The voice coils are the same size, just different dustcaps, their DC resistance readings were within close range, and they sound the same in my testing.  Also, one has aluminum dust shields on the Alnico magnet’s U-shaped cover, the other used reinforced fabric.  For your review, I’ve attached photos of the woofers after I finished refurbishing the suspension with the correct-style, inverted-roll foam surrounds, directly below.
The other differences between the speakers are of even less consequence but nevertheless interesting. The input panel cutout is lower on the early speaker, but an equally proportional 6” in distance from its respective end.   This tells either me the woofer and transducer cutouts were made opposite unintentionally
or
by the later speaker the higher input panel positioning had been decided?  The latter could also be true of the increased center cap size (bigger cap looks better, stronger without changing anything)?  Lastly, there is a difference in the grille panel frame cutouts; one is essentially a full perimeter cut, rounded beneath the woofer, the other has a circular woofer opening and full-width rectangular opening for the AMT.  I lost track which came from which on that one!
Regarding the woofers, many speaker companies, domestic and foreign, used foam for their woofer surrounds from the early 1970’s through 1990’s.  Foam offers superior excursion to coated linen and rubber surrounds, but invariably rots and falls apart in 12-20 years no matter what climate you live in. These woofers were no exception; the surrounds were cracked throughout with pieces missing.  And, as I’m sure most know, proper cone suspension is very important—if you play woofers with faulty surrounds for too long they’ll start to rub the voice coils and ruin them in a short time. As such, surround replacement is critical for correct function.  So, I replaced the aged original polyurethane foam surrounds with the correct inverted-roll, flat inner-attach polyether surrounds.
Some of you have replaced woofer surrounds before, so you know it’s a time-consuming process that takes a great deal of patience and a steady hand. First, I removed one paper chip flange gasket (the early woofer did not have one) then thoroughly cleaned the basket flanges and cone edges to remove the old gummy foam and stubborn factory adhesives, which takes some time to do properly, and then glued the inner surrounds to the cones.  Next, I glued the outer surrounds to the basket flanges after verifying no coil rub.  Lastly, I applied
new
hard paper chip-style gasket segments for proper appearance.  I allowed overnight drying of the acrylic glue between each of the steps to achieve the perfect results you see here.  Now these woofers in great shape once again—perhaps even better than new with the modern foam surrounds!
Most importantly, the woofers were fully tested after the new surrounds were installed and sound terrific—very strong and clear with fast, detailed lower midrange coverage and solid low-end as rated to a respectable 40Hz.  Installed in the AMT 5 speakers alongside the amazing Heil AMT’s reinforced a successful speaker restoration.
True to their reputation with those "in the know," the AMT 5’s sound amazing.  The Heil transformer’s clarity, imaging, and musical detail are simply spectacular.  I am able to detect instruments, which I’d never noticed before, in pieces that I’ve heard for years.  Though rated to 20kHz, it’s the transparency of their output that puts them above other high-end tweeters that claim a higher ceiling.  The Heil AMT is a driver that must be heard to be believed.  It’s the real deal!
What’s more, the AMT 5’s +/- inputs are sturdy binding post terminals that accommodate banana plugs, pin connectors, or raw speaker cable.   Plus, they have a brilliance control for adjusting the AMT to varying room conditions, but I always left it on the “normal” setting.  Also, the AMT’s are fuse-protected against excessive input power or clipping.  And, I recommend putting the AMT 5's on stands to bring the Heil to typical seated ear level.  Lastly, in the period magazine review that follows, I believe they're wrong about being able to rotate the Heil for horizontal speaker placement.  On these first-year AMT 5 speakers, it is not possible.
As pictured and described, this uncommon, great-sounding pair of ESS AMT 5 speakers is offered at a competitive price.
In exchange for this handsome investment, the new owner will enjoy their exceptional sound quality and timeless appearance for many years to come!
Terms of Sale
:
I encourage prospective buyers to ask any questions they may have about this pair of ESS AMT 5 speakers as there are
no returns, refunds, or claims considered
for this listing. These are very high quality speakers, but they’re also over 45 years old.  There’s an inherent risk to buying pre-owned audio equipment, even from the most respected companies, as some parts can suddenly fail due to age degradation with no warranty recourse.  What’s more, I have no idea in what manner the new owner will be putting these speakers to use, what degree of experience they have with audio equipment, or the quality and condition of the equipment the speakers will be connected to.  Also, I pack items
very
securely, and full insurance coverage will be included in the shipping/handling cost, but will not be held liable for rough/negligent handling in the shipping process
nor
fall prey to a “parts switching” scheme of any sort.  These are extremely well-built speakers, so I don’t foresee any problems, but nevertheless needed to state the above.
If this makes you skeptical, please take a look at my feedback pages and you won’t be.  I’ve been an
eBay member for over 22 years
and have served thousands of satisfied audio customers.  And, I’d like
you
to be the next one!
A note on shipping
:  At nearly 40 pounds each, and sporting a substantial profile, it will take me several days to devise and implement a plan to get these ESS AMT 5 speakers to the new owner
safely
.  They will have to go in two separate large boxes, each lined with dense foam panels and/or other protective materials I deem fit to ensure no disappointments upon arrival.  The quoted shipping cost is for two (2) packages and will cover carrier charges, full insurance coverage, and materials cost.
Local pick-up
is fine, actually
preferred
, for those in the Chicago-Milwaukee metro area (or farther if you’re willing to make the drive).  We’re located about 35 miles north of downtown and some 20 miles south of the WI State line at Kenosha.  For those interested in pickup, please contact me so that I can discuss that option with you.
Payment is due at checkout
. U.S. lower 48 mailing addresses will pay 0.00 for
very
carefully packed shipping via U.S. Postal Service
or
FedEx with tracking, delivery confirmation, and
full insurance coverage
.
AK, HI, PR, APO & U.S. Territories must pay additional charges for U.S. Postal Priority Air Mail
(even though checkout might still show FedEx Ground, a service not offered to those destinations for obvious reasons).
Lastly,
no international purchases
for this listing, U.S. buyers only.
Thanks for looking, and I look forward to doing business with one of you!