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Area 51

Rare and Special materials not available elsewhere


Techniques explained, parts, suppliers and weird shit.
  • Introduction

    The Quad ESL was the world's very first full range, commercially available electrostatic loudspeaker. In spite of its great antiquity (some 50 years old to date) it was voted the "Greatest Hi-Fi Product of All Time" by Hi-Fi News and record review in the January 2000 issue of that journal. Read More
  • FixIt

    The Quad Electrostatic Loudspeaker is one of those very, very few things that you may own which is about 20 to 30 years old, that you would want to spend any time restoring to original condition. However, it seems that there's quite a few folks out there who still prize Read More
  • Parts

    All the very special materials like diaphragm film (6 micron) and coatings - CALATON and ELVAMIDE - have 'moved' to Area 51. You'll find special 'kits' there also, along with dust cover material and the pride of the site, some tensilised 6-micron treble panel film and 12-micron PVC bass panel film, at Read More
  • Amplifiers

    If there was ever a contentious topic of discussion not directly involved with the Quad electrostatic speaker itself, then this is it. I think I have seen and read more correspondence on the matter of amplifiers than everything but the coating material on the diaphragms and the "Did they coat Read More
  • Patents

      Filed: July 15, 1955 U.S. Patent 3,008,013Granted: November 7, 1961 David Theodore Nelson Williamson, Edinburgh, Scotland assigned rights to Ferranti Ltd., London. Peter James Walker of Huntingdon, England."Electrostatic Loudspeakers" Read More
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Aurealis Audio

 A Great 

Aura Turntable

The Aura

A Great Turntable

Popular Articles

  • Introduction >

    The Quad ESL was the world's very first full range, commercially available electrostatic loudspeaker. In spite of its great antiquity Read More
  • Christian Steingruber >

    Amplification for Quads - Fifth Edition by Christian Steingruber "All amplifiers sound the same" - Peter Walker "Amplifiers DO sound different" - Martin Read More
  • Walker & Albinson 1976 U.S. >

    Filed: January 10, 1975U.S. Patent 3,970,953Granted: July 20, 1976 "Distortion-Free Amplifiers"Peter James Walker and Michael Peter Albinson Read More
  • Wiring Diagrams >

    You've taken the old Quads apart and Holy Shit(!) Batman, the wiring is NOT colour-coded!! What can you do? The Read More
  • Top Components >

    There are very few components that I would unreservedly trust to put in my own Quads. Pre-built components, that is. Read More
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Interviews and Reviews

  • icon Walker 1978
  • icon AES Lecture
  • icon Mike Albinson
  • icon Hi Fi News 1957
  • icon Quad 410
  • icon Audio Critic 1980
  • icon Sound Practices 1994
  • icon Classic Hi Fi 1996
  • icon The Listener 1998
  • icon The Audiophile 1998
  • icon OTLs and Quad
  • icon Futterman OTL
  • icon Gang of Five

'Audio Amateur'

Interviews Peter Walker at the Quad Factory in 1978

TAA: What do you consider to be the important goals of a good audio reproduction system what ought a good audio reproduction system do?

PW: Well, perhaps this reflects my age (62 at the time of the interview), but I am still in favour of documentary type reproduction - an orchestra plays on a stage

Read More

Click the images below (l to r) in succession to see Walker's address to the U.K. Audio Engineering Society in 1979 on the Quad ESL 63

Read More

ACOUSTICAL MANUFACTURING's Mike Albinson, co-designer of the revolutionary Quad 405 power amplifier, and outspoken critic of many current fashionable amplifier theories, is our subject this month.

Practical Hi-Fi: The Quad 405 represents something fairly unique in modern Hi-Fi amplifier design. What led you to the concept of feed-forward instead of the more normal feedback?

Mike Albinson: Difficult question, but I have a stock answer to

Read More

The Quad Electrostatic Speaker

by Ralph West

The recent appearance of a full range ESL designed and produced by a well-known manufacturer specialising in high quality reproduction, was bound to cause considerable comment and speculation. This speaker, the "Quad" electrostatic, is now in production, and we are pleased to present our readers with a full review of a specimen drawn from current production. The makers

Read More

No, Quad have not capped off their recent release of the ESL 63 speaker with a new amplifier! The 410 is in fact the designation given to the 405 power amplifier when its channels are bridged together to give a mono amplifier of effectively 180 watts. In fact, it is even possible to bridge a pair of these 410 amplifiers to give a mono amplifier

Read More

The AUDIO-CRITIC Volume 2, Number 3 (Spring to Fall 1980) wrote:


"This all-time classic needs no introduction to any audiophile who knows enough to read equipment reviews at all. It has survived virtually unchanged for a quarter of a century (the manufacturer claims there have been no changes whatsoever, large or small, but we take that with a grain of salt); we,

Read More

Sound Practices - 1994

The Quad Electrostatic Loudspeaker

by Haden Boardman / Mellotone Acoustics

A good electrostatic has something special, a magic spell that weaves itself over you. Critics (of which there are few) moan on ~bout "won't play rock" or "only for string quartets". Ask these plaintiffs what system they have, or what kind of speakers, and the usual response is some old west coast monster.

Read More

Hi-Fi News and Record Review, UK.

Classic Hi-Fi, Jun 1996

Restoration Drama by Ken Kessler

In late 1995, the Bugatti Owners' Club produced facsimile reprints of all of the issues of the Club Magazine, Buganacs, issued before WWII. It was telling to read articles from, say, 1938, about the trials and tribulations of working on even 10 year old vehicles, at a time when the

Read More

The Quadfather

In the beginning, there was the Quad ESL, the world's first full-range electrostatic loudspeaker.

An appreciation, by Chris Beeching

Quad ESL loudspeaker: available used for between $600 and $2000 per pair and up, depending on condition. Originally manufactured by Quad Electroacoustics, Huntington, England.Surely the venerable Quad speaker is one of the most enduring of all quality hi-fi products ever made.Since it took the

Read More

Quad ESLs:Then and Now

Blair Roger

Can a loudspeaker be all things to all people? Probably not, but the Quads take a damn good shot at it and I'll dispute anyone who says otherwise.


Peter Walker and his engineering team have been unconventional and pragmatic thinkers since S. P. Fidelity Sound Systems was founded in 1936. By 1938 they were manufacturing a portable public

Read More

The history of this amp's circuit starts twenty five years ago when Julius Futterman, understanding the limitations of the output transformers. patented an Output Transformerless design. The clarity of the sound has been unsurpassed to this day and a cadre of serious music listeners has remained steadfast to the genius of Julius Futterman. The man was the embodiment of integrity in the audio world and

Read More

Letter to the Editor

(Julius Futterman)

"I am pleased with your evaluation of the sonic virtues of the H-3aa power amplifier but do take exception to two of your assertions :

The power tubes I use (6LF6) are being manufactured in the USA by GE and Sylvania. They are also being made in Japan and Yugoslavia. I have been informed that they will be around for

Read More

Gang of Five

Gary Jacobson

N.B. This article is about 10 years old. Therefore an historical document!

Any advice and observations that it contains should therefore NOT be taken as being, in any way current.


Madness strikes at all hours of the day and night, so I can’t tell you exactly when it occurred to me to assemble a collection of treble panels from

Read More

Original ESL Patents

  • icon Masolle 1921
  • icon Lee 1925
  • icon Depew 1926
  • icon Hahnemann 1928
  • icon Hartley 1928
  • icon Kellogg 1929
  • icon Rauser 1930
  • icon Rauser 1931
  • icon Vogt 1930
  • icon Vogt 1928
  • icon High 1930
  • icon Kellogg 1929/2
  • icon Etablissements S.M. 1946
  • icon Janszen 1949
  • icon Kock 1951
  • icon Curry 1953
  • icon Parker 1954
  • icon Williamson 1955
  • icon Williamson 1957

Filed: November 28, 1921
U.S. Patent 1,550,381
Granted: August 18, 1925

Joseph Masolle, Hans Vogt and Josef Engl assignors to Tri-Ergon Ltd., of Zurich, Switzerland
"Electrostatic Telephone"

Referenced by Walker and Williamson in
U.S. Pat. 3,008,014.

Read More


Filed: May 2, 1925
U.S. Patent 1,622,039
Granted: March 22, 1927

Frederick W. Lee, Owing Mills, Maryland.
"Apparatus for and Method of Reproducing Sound".

Referenced by Walker and Williamson in U.S. Pats. 3,008,013 & 3,008,014.

Read More

Filed: February 12, 1926
U.S. Patent 1,631,583
Granted: June 7, 1927

John Depew, of New York.
"Capacitatively Actuated Loudspeaker".

Referenced by Walker and Williamson in U.S. Pat. 3,008,014

Read More

Filed: March 24, 1926
U.S. Patent 1,674,683
Granted: June 26, 1928

Walter Hahnemann, Kitzberg, Germany, assigned rights to Lorenz Aktiengesellschaft.
"Arrangement for Uniform Electrical Sound Transmission".

Referenced by Walker and Williamson in U.S. Pat. 3,008,013

Read More

Filed: June 6, 1928
U.S. Patent 1,762,981
Granted: June 10, 1930

Ralph V.L. Hartley of South Orange, N.J. assigned rights to Bell Telephone Labs., N.Y.
"Acoustic Device"

Referenced by Walker and Williamson in U.S. Pats. 3,008,013 & 3,008,014

Read More

Filed: Sept. 27, 1929
G.B. Patent 346,646
Granted: April 16, 1931

Edward Washburn Kellogg, Schenectady, N.Y. assigned rights to General Electric Co. N.Y.
"Production of Sound"

Indirectly Referenced by Walker and Williamson in U.S. Pats. 3,008,013

Read More

Filed: February 12, 1930
G.B. Patent 348,573
Granted: May 12, 1931

Albert Rauser and Wilhelm Steuer, of Kottbuser-Ufer 39/40, Berlin, S.O. 26
"Improvements Relating to Electrostatic Loud-speakers".

Referenced by Walker and Williamson in U.S. Pat. 3,008,014

Read More

Filed: June 1, 1931
G.B. Patent 370,248
Granted: April 7, 1932

Albert Rauser and Wilhelm Steuer, of Kottbuser-Ufer 39/40, Berlin, S.O. 26
"Improvements in Electrostatic Loud-speakers".

Referenced by Walker and Williamson in U.S. Pat. 3,008,014

Read More

Filed: Sept. 8, 1930
G.B. Patent 372,649
Granted: May 12, 1932

Hans Vogt, Genthinerstrasse 17, Berlin, W. 35, Germany.
"Improvements Relating to the Insulation of Fixed Electrodes of Electrostatic Loudspeakers"

Indirectly Referenced by Walker and Williamson in U.S. Pat. 3,008,014

Read More

Filed: Sept. 15, 1928
U.S. Patent 1,881,107
Granted: Oct. 4, 1932

Hans Vogt of Berlin-Wilmersdorf, Germany.
"Sounding Condenser"

Referenced by Walker and Williamson in U.S. Pat. 3,008,013. Also ref: GB Patent 322,744 with 17 claims, granted December 10, 1929

Read More

Filed: July 30, 1930
U.S. Patent 1,930,518
Granted: October 17, 1933

Jurjen S. High of Camden, N.J. assigned rights to Westinghouse Electric and Manufacturing Co. Pennsylvania.
"Electrostatic Loudspeaker"

Referenced by Walker and Williamson in U.S. Pats. 3,008,013 & 3,008,014

Read More

Filed: Sept. 27, 1929
U.S. Patent 1,983,377
Granted: December 4, 1934

Edward Washburn Kellogg, Schenectady, N.Y. assigned rights to General Electric Co., N.Y.
"Production of Sound"

Referenced by Walker and Williamson in U.S. Pat. 3,008,013. Also ref: GB Patent 346,646 which pre-dates this grant of patent on the same device.

See prior citation of E.W. Kellogg.

Read More

Filed: April 9, 1946
G.B. Patent 610,297
Granted: Oct. 13, 1948

Etablissements S.M. Body Corporate of 26 Rue de Lagny, Paris.
"Improvements in Electrostatic Microphones and Loud-speakers"

Referenced by Walker and Williamson in U.S. Pat. 3,008,013.

Read More

Filed: October 5, 1949
U.S. Patent 2,631,196
Granted: October 5, 1953

Arthur A. Janszen, Cambridge, Mass.
"Electrostatic Loud-Speaker"

Referenced by Walker and Williamson in U.S. Pats. 3,008,013 & 3,008,014.

Read More

Filed: December 12, 1951
U.S. Patent 2,796,467
Granted: June 18, 1957

Winston E. Kock, Basking Ridge, N.J., assigned rights to Bell Telephone Labs., N.Y.
"Directional Transducer"

Referenced by Walker and Williamson in U.S. Pats. 3,008,013 & 3,008,014.

Read More

Filed: December 11, 1953
U.S. Patent 2,855,467
Granted: October 7, 1958

Paul Curry, New Haven, Connecticut assigned rights to Curry Electronics Inc., New Haven, Conn.

Referenced by Walker and Williamson in U.S. Pat. 3,008,014.

Read More

Filed: November 29, 1954
U.S. Patent 2,864,899
Granted: December 16, 1958

Henry W. Parker, Flushing, N.Y.

Referenced by Walker and Williamson in U.S. Pat. 3,008,014.

Read More


Filed: July 15, 1955

U.S. Patent 3,008,013
Granted: November 7, 1961

David Theodore Nelson Williamson, Edinburgh, Scotland assigned rights to Ferranti Ltd., London. Peter James Walker of Huntingdon, England.
"Electrostatic Loudspeakers"

Read More

Filed: September 12, 1957
U.S. Patent 3,008,014
Granted: November 7, 1961

David Theodore Nelson Williamson, Edinburgh, Scotland assigned rights to Ferranti Ltd., London. Peter James Walker of Huntingdon, England.
"Electrostatic Loudspeakers"

Read More

ESL 63 Patents

  • icon Kellogg 1929
  • icon Shorter 1940
  • icon Dome 1941
  • icon Harry 1943
  • icon Stolaroff 1948
  • icon Wilkins 1954
  • icon Wilkins 1956
  • icon Macdonald 1958
  • icon Wright 1958
  • icon Wang 1967
  • icon Walker 1970

Filed: September 27, 1929
U.S. Patent 1,983,377
Granted: December 4, 1934

Edward W. Kellogg "Production of Sound"

Referenced by Walker in U.S. Pat. 3,773,984.

Read More

Filed: February 21, 1940

G.B. Patent 537,931
Granted: July 14, 1941

Donovan Ernest Lea Shorter
"Improvements in Electrostatic Loudspeakers"

Referenced by Walker U.S. Pats. 3,773,984.

Read More

Filed: January 28, 1941
U.S. Patent 2,302,493
Granted: November 17, 1942

Robert B. Dome, Bridgeport, Connecticut
"Amplifying System".
 Referenced by Walker in U.S. Pat. 3,773,984.

Read More

Filed: June 24, 1943
U.S. Patent 2,387,845
Granted: October 30, 1945

William R. Harry, Summit, New Jersey
"Electroacoustic Transducer".

Referenced by Walker U.S. Pat. 3,773,984.

Read More

Filed: December 18, 1948
U.S. Patent 2,634,335
Granted: April 7, 1953

Myron B. Stolaroff, Redwood City, California assignor to Ampex Corporation
"Magnetic Recording System with Negative Feedback System."

Referenced by Walker U.S. Pat. 3,773,984.

Read More

Filed: May 19, 1954
U.S. Patent 2,843,671
Granted: July 15, 1958

Charles A. Wilkins and Herbert Sullivan, New York
"Feed Back Amplifiers"

Referenced by Walker in U.S. Pats. 3,773,984

Read More

Filed: August 29, 1956
U.S. Patent 2,905,761
Granted: September 22, 1959

Charles A. Wilkins, New York.
"Control of Amplifier Source Resistance"

Read More

Filed: September 9, 1958
U.S. Patent 3,061,675
Granted: October 30, 1962

James Ross Macdonald
"Loudspeaker Improvement"
Claims 1-5], [Claim 5 ]. Diagrams:[Sheet 1] [Sheet 2]
Referenced by Walker in U.S. Pat. 3,773,984.

Read More

Filed: December 10, 1958
U.S. Patent 3,135,838
Granted: June 2, 1964

William M. Wright, Boston Mass.
"Electrostatic Loudspeaker"

Referenced by Walker in U.S. Pat. 3,773,984.

Read More

Filed: May 18, 1967
U.S. Patent 3,542,952
Granted: November 24, 1970

Chien San Wang, Denver, Colorado
"Low Distortion Signal Reproduction Apparatus"
Referenced by Walker in U.S. Pat. 3,773,984.

Read More

Filed: November 3, 1970
U.S. Patent 3,773,984
Granted: November 20, 1973

Peter James Walker of Huntingdon, England.
"Electrostatic Loudspeaker with Constant Current Drive"

Read More

Quad 405 Patents

  • icon Ketchlidge 1956
  • icon Walker & Albinson 1976 U.S.
  • icon Walker & Albinson 1976 G.B.

Filed: September 26, 1952
U.S. Patent 2,751,442
Granted: June 19, 1956

Raymond W. Ketchlidge

"Distortionless Feedback Amplifier"
Referenced by Walker in U.S. Pat. 3,773,984.

Read More

Filed: January 10, 1975
U.S. Patent 3,970,953
Granted: July 20, 1976

"Distortion-Free Amplifiers"
Peter James Walker and Michael Peter Albinson

Read More


Filed: January 10, 1975
U.S. Patent 3,970,953
Granted: July 20, 1976

"Distortion-Free Amplifiers"
Peter James Walker and Michael Peter Albinson

Read More

You've decided to repair some damage, or refurbish the whole speaker, but first(!) you need to take it apart, properly. Take it easy, since anything you damage is likely to be expensive or time consuming to fix, or both. This section will explain how to take the speaker apart with the minimum fuss and bother.

Firstly See...



Grille Removal:

The front grille is removed as follows:

  • Remove the three screws retaining the side rails, along with their washers.
  • Remove the staples that hold the grille to the wooden frame at the sides.
  • Remove the 10 to 12 small wood screws from the front bottom edge (underneath) of the front grille.
  • Carefully lift the grille in a smooth arc, forwards and outwards, being patient at all times lest you bend the grille (it's only expanded aluminium)

The rear grille is removed as follows:

  • Remove the twenty, or so, small wood screws around the periphery of the wooden frame at the rear, along with their washers.
  • Remove the rear grille, being careful not to puncture a dust cover or yourself!


EHT Block Disconnection:

To disconnect the EHT block, do the following:
(all directions as viewed from the rear of the speaker)
(The speaker must be off for at least 2 hours!!)

  • Place a stiff piece of cardboard, or a rolled up cloth, between the EHT block and the bass panel to prevent any solder melting the dust cover, or worse.
  • Using a standard 20 Watt iron, de-solder, from left to right: the thick red wire, the thin red wire, and the thin black wire. This disconnects (physically and electrically) the bass panel 6kV line (thick red), the treble panel 1.5kV line (thin red) and the Ground/Earth wire (thin black) to the audio transformer.
  • Do not disconnect the other wires on the EHT at this time, they only connect to the mains transformer, which is physically part of the cage assembly on which the EHT block is fixed. You will be able to remove all the large assemblies with these latter wires in place.


EHT Assembly Removal:

(all directions as viewed from the rear of the speaker)
(The speaker must be off for at least 2 hours!!)
To remove the Mains Transformer cage and EHT unit (on top) from the frame, do the following:

    • Locate the four (4) retaining bolts under the right, rear of the frame and unbolt them. These bolts do have nuts above the frame, which may need to be held with a spanner or pliers.
    • The Mains Transformer cage and EHT block can now be completely removed from the speaker.


Audio Transformer Disconnection:

(all directions as viewed from the rear of the speaker)
(The speaker must be off for at least 2 hours!!)
The audio transformer is the large 'can' on the left, rear of the speaker. To remove it, and disconnect the treble and bass panels, do the following:[Top]

  1. Place the speaker on a stand, or up on two bricks, or whatever, so that you can easily work underneath it without grovelling on the floor too much.
  2. Find the four large bolts (pan head) underneath the left side of the speaker that secure the audio transformer.
  3. Remove these bolts. There are no corresponding nuts. The bolts screw into tapped brass blocks mounted inside the audio transformer. When the transformer comes loose, be careful it doesn't slide about as it is very heavy and can damage wiring and panels.
  4. Turn the audio transformer (carefully!) upside down. This requires some fiddling about because of the restricted wiring loom, but it can be done. There is just enough free play in the wires. You should end up with the audio transformer sitting in its usual spot, only upside down.
  5. Now, examine the underside in detail. If you see a whole lot of bees wax (brown/yellow gunk) then this device has never before been touched since it left the factory. You will see several wires entering through a rubber grommet at the front of the transformer housing. The thin brown and blue wires go to the front and rear plates of the treble panel. The brown wires connect to the centre strip and the blue wires to the other two strips in the treble panel. The thick white and black wires take audio signals to the bass panels. A schema of the underside of the audio transformers of each type is shown below:

  1. De-solder the wires from the solder posts, and remove them carefully through the rubber grommet. At this point, you will be able to take the heavy transformer unit out of the frame, and give yourself more room to move. You may need a hefty soldering iron for
  2. Take a very careful note of each wire's position. If you cannot read this simple schema, or you don't trust yourself to remember the wiring pattern, then LABEL each individual wire, and where it goes with a stick-on tab, or something. Colour code them with permanent marking pens, and write down the colours would also work well. If you re-wire incorrectly, the speaker will: run out of phase, not run at all, emit smoke!
  3. this - about 40 Watts should do.

End Note: If, for any reason, you need to remove the bees wax, then use a heat gun. I use a 1600 Watt variable setting gun that can be set as low as 400 Watts. This gives a lot of control, since you can keep the gun moving!!


Treble Panel Removal:

(The speaker must be off for at least 2 hours!!)
To remove the treble panel, do the following

  1. Double check that the thin red wire to the EHT, the two thin brown, and two thin blue wires to the audio transformer have been de-soldered.
  2. The thin red wire needs to be pulled back through the frame supports (large inverted V-blocks) to the audio transformer side of the frame.
  3. Now go to the front of the speaker, and you will see an aluminium retaining bracket between the two bass panels at top and bottom of the treble panels. These are folded aluminium of about 8 gauge. They are in the form of a U-channel, and if you look down into them you will see the heads of a couple of wood screws. Remove these screws.
  4. Remove the two aluminium brackets, top and bottom. This may require gentle(!) leverage with a screw driver. The panels are now mechanically unrestrained, but they will sit where they were put all those years ago.
  5. Move to the extreme right hand side of the wooden frame and insert a suitable flat bladed screwdriver blade between the wooden frame of the speaker and the bass panel frame. Gently lever the bass panel towards the centre. You will notice that it slides out of a couple of other aluminium brackets towards the edge of the speaker frame. It is not necessary to touch these brackets.
  6. Do the same to the other bass panel. The aim is to have them both loose, not removed from the frame at this stage.
  7. Set each bass panel at a slight angle to the treble panel, like a pair of opening doors. N.B. The panel dust covers may be stuck together after all this time under pressure - lever them gently apart.
  8. Now you will be able to remove the treble panel carefully, with its associated loom of wires, from the front of the speaker.


Bass Panel Removal:

(The speaker must be off for at least 2 hours!!)
To remove the bass panel(s), do the following:

  1. Do not remove the wiring from the frame unless you intend to totally rewire the speaker, or you are going to re-spray the wooden frame - this saves time and effort. These instructions simply cover the removal of the bass panel(s).
  2. Label the wires you remove! The order of the wires, as viewed from the rear is: BACK of Bass panel is connected to the thick white wire on the LEFT post; FRONT of the bass panel is connected to the thick black wire on the RIGHT post; and, the 6kV EHT line (thick red wire) is connected to the CENTRE post.
  3. Place a piece of cardboard between the small phenolic connection board and the plastic of the dust cover, to protect against blobs of solder melting their way into the panel.
  4. Using a standard 20 to 30 Watt soldering iron, de-solder the three wire at the bottom of each bass panel. You will find that with an original panel the wire was wound around and around and around....the post several times to get the smooth connection needed for the high voltages involved.
  5. Do not attempt to de-solder wires from the actual panel itself at this time. This is a delicate task, and will be described elsewhere. At this point you should be able to manoeuvre the bass panel(s) completely free of the frame.



Unlike an EHT block, or other parts of the speaker, it doesn't take too much diagnostic skill or an involved process to see if the dust covers have damage. They will show splits and tears, plastic 'sticky' tape mends and so on. If they feel a little brittle, as if the next cockroach that walks over them would split them wide open, then it is probably time to replace them. Hey, if you disassembled the speaker the first time (Disassembly Section) without making a split or a hole in a dust cover, then I am awed, to say the least. You need either a heat shrink film of 12 mm (or less) gauge, or some 12 mm (or less) gauge Mylar®. Quad originally used a 6 mm Mylar® for the Treble Panel and a 12 m m Saran® film for the bass panel covers. It is possible to get P.E.T. in gauges down to 0.9 mm, but it is doubtful that it would be robust enough in this application. It is also can be fiendishly expensive! You can also use the tensilised P.E.T. from Area 51 to make a treble panel dust cover identical to the original.

In general, the material of choice for many folks is 12 mm Mylar®, but I use 12 mm heat shrink film that was designed for light duty packaging in the computer industry. I have heard of some people using sandwich wrap, OK, it's a Saran® wrap of a light gauge. The width of the film needs to be about 400mm, and this will cover both Treble (easily) and Bass Panels, leaving enough around the edges to work with easily.

To replace a dust cover, do the following:

  1. Remove the panel(s) from the speaker - See the Disassembly Section.
  2. Get out the vacuum cleaner, if you haven't already, this will get messy.
  3. Once the panel is out, you will see a five layer 'sandwich' of bits and pieces, held together with a (very old) P.V.C. tape. The outer "layers" of the sandwich are light wooden frames, holding the dust cover plastic.
  4. Using a hobby knife (Stanley® knife) or other razor sharp knife, slit the tape around the perimeter. Be very careful that you don't cut into the panel, as it's only plastic, or the light wood frame. Both of these unnecessary disasters can happen if you're a little too eager with the knife. In the process a lot of old dried up glue dust, wood dust, oxides, and sundry light particles will be released. Be warned if you are an asthmatic! Vacuum as you go - Nature may abhor a
    vacuum, but Quads don't.
  5. Strip the tape, the plastic film, and that gungy brown adhesive detritus from the frame. How you do this is up to you. It will probably flake off. Methylated spirit is a help in dissolving the old adhesive. Very fine (600 grit) sand paper can be useful on the wooden frame, too. You just want the frame to be clean, smooth and in one piece when you're finished.
  6. Cut a piece of your chosen dust cover plastic equal to the length of the panel, plus about 75 mm (3 inches) over each end. If you're using 400 mm wide material off the roll then you'll have enough to play with at the sides automatically.
  7. Lay this flat on a smooth laminex surface, or similar. Gently smooth out the major wrinkles and tape the film at the corners of the rectangular piece and the mid-points. No real tension needs be applied.
  8. Apply your glue of choice to the wooden frame. I use a fast-drying, pressure sensitive spray-on glue that's available in every five and dime. It doesn't dry 'hard' and costs about $AUD5-00 for a 350g spray can. This will do a lot of dust covers. I would estimate a couple of dozen per can.
  9. Immediately centre the frame glue-side down on the plastic.
  10. Wrap any excess plastic film at the edges around the frame, away from the glued side. Weight it, if necessary until the glue dries. I find that I can have the frame covered in about 5 minutes from the time I cut out the film to the time I put the frame aside for later use.
  11. Trim any excess film around the edges with a very sharp (razor) knife.
  12. Do NOT heat shrink the film at this time! It is far better to wait until the frame is taped back onto the panel during final assembly. These frames do not resist tension at the mid-point at all well, and you will pull them out of shape with heat shrinking at this stage.
  13. When it does come time to heat shrink, I use a hair dryer, since the film I use is a specialised film designed to shrink at moderate heat levels. If you use Mylar® then you will need to use a heat gun, as Mylar® will not heat shrink well with a hair dryer - doesn't put out enough heat.
  14. Put your re-covered dust covers in a safe place for later use.
  15. N.B. Heat shrinking is most critical with the Treble Panel Dust Covers and you must not leave even small "ripples" in the finished cover. This is because the high frequencies it operates at will cause the dust cover to "rattle" or "buzz" if there are even small imperfections. The Treble Panel Dust Covers even have small bolts and felt washers to damp any buzzes and rattles in the dust covers at high frequencies. The Bass Panel Dust Covers are not so critical and even a few wrinkles generally cause no major problems.


Wait a minute! Why are you 'fixing' the EHT block? OK, the speaker is old, but check the voltages first. You will need an electrostatic voltmeter - fiendishly expensive - or a high voltage probe such as technicians use to measure the HT circuits in televisions and other CRT devices  - See Parts Section

The use of a high voltage probe has some caveats, but is the only device you are readily likely to lay hands on to measure these voltages at the minute currents present. Click image below to see larger EHT wiring image.


EHT Checks:

To check the specification of the EHT, do the following:

  1. Disconnect the thick red wire and the thin red wire (as a minimum) from the EHT block. This is described more fully in the Disassembly... Section.
  2. The EHT must now be plugged into the mains for this test, and allowed to charge for 5 to 10 minutes. The "low" voltage mains terminals that are now exposed carry up to 610 Volts, with sufficient current to be fatal!
  3. Do check the 610 and 590 Volt tags on the secondary of the mains transformer, making sure that they are within a few % of the stated values. If these voltages are "off" then everything else that depends on them will clearly be amiss also.
  4. Connect the high voltage probe to a standard multimeter (10MW input) as directed by the manufacturer of the probe. Ground/Earth the probe to the same earth point as the Mains Transformer, (clip to the terminal where the THIN black wires connect to the block).
  5. Set your DVM to 'auto ranging' or to a high range. The probe manufacturer will have indicated the scaling factor when connected to a standard 10MW input, (usually 1000:1).
  6. Touch the HT probe to the terminal post on the EHT block where the thick red wire was connected. The reading won't be 6kV +/- 7%, that is between 5 580 Volts and 6 420 Volts!! Why not? The HT probes we generally use in the absence of a true electrostatic voltmeter do not have sufficiently high input resistance, and too much current flows. Consequently the voltage drops and you do not measure 6kV out of a "good" EHT block. A "good" rectifier block with no panels attached will read around 3.9 to 4kV with a HT probe. With good bass panels connected, the reading will rise to 4.3 to 5kV. The resistance of the panels is now in circuit. If you get a reading lower than 3.6kV then the panels are likely leaky, in which case they'll probably hum anyway. Take note of the readings immediately after contact is made, as it will tend to drain the supply very quickly. Remember, these probes do drain significant current (mA) in this context. Another caveat is that a faulty supply can give a high reading due to an open circuit component in the multiplier chain -usually a blown capacitor - no, they are not "good for life" as some authors surmise. { Ron Best of One Thing Audio, Coventry, England reports that he has seen faulty EHT units measure as high as 10.6kV (!) with a true electrostatic voltmeter. Thanks to Ron for the above servicing details also. If you live in England, he is the man to see to get your Quads serviced.}
  7. Similarly, touch the terminal post to which the thin red wire was connected. The reading should be 1.5kV +/- 7%, that is, between 1 395 Volts and 1 605 Volts. Again, your meter, connected to the 1000:1 probe should be showing 1.4 to 1.6 with the probe in circuit.

If these measurements fall within the ranges stated, then there should be no real need to disassemble the EHT block any further, and it can be put into service, as is. If any under-voltage conditions are noted when the panels are connected, then leakage from the panels has to be suspected. This leakage will manifest itself as either visible corona on terminals, or leakage to the frame from the stators themselves. In the case of bad leakage, the panels will hum at about the mains frequency.

If these measurements are under the minimum, then it is time to rebuild the EHT block. The low voltage is likely being caused by the breakdown of the diodes used in the ladder circuit in this block. The capacitors will likely be OK, but you can replace those too, if you like.

If the speaker is really old (50's, 60's, early 70's) then it will very likely have a single epoxy block rectifier fitted. If this is under specification, you can only throw it away, unfortunately. It is possible to copy the circuit on a small piece of breadboard, insulate it with anti-corona lacquer and remount this. Alternatively, you can buy Sheldon Stoke's circuit boards, or make your own, if you're keen enough.


EHT Rebuild:

If the speaker is of later vintage, the EHT block will be composed mainly of a small box made of phenolic plastic "board", such as used in the 'old days' for circuit boards. This box is filled with bees wax, to prevent high voltage leakage to the atmosphere (corona). This type of unit can be completely serviced, as follows:

  1. Detach the EHT block from the mains transformer cage. This requires the removal of two small screws that screw into the block from the mains transformer side.
  2. Place the EHT block in a small metal pan. The pan should be just large enough to hold the block lying on its side, so that when we melt the wax out, we won't have to scrape a thin layer of the stuff out of the pan. It is also easier to re-melt the wax, if you have to, in a small pan.
  3. Melt the wax out with a heat gun. I use a variable 1600 Watt gun, set to about half way. Some folks advocate placing the whole thing in an oven. This has four problems: you cannot see what is going on; you cannot control the heat as easily; you can burn the plastic box easily; and, it takes longer, and costs more. If you are applying too much heat with a heat gun, it is a simple matter to move the gun a little farther away. The big plus is that you can see what is happening, and are less likely to cook (literally) the small circuit board.
  4. Remove the small circuit board with pliers, or tongs!! IT'S HOT!!
  5. Allow the unit to cool down, and examine all the parts. You will see two resistors, 16 diodes, and 8 x 3kV x 0.01m F capacitors.
  6. Re-wire the circuit with new parts. Generally, 2 Watt metal film resistors are more than adequate (330kW and 2.2MW), along with 1N4007 diodes, and capacitors rated for 3kV (or higher) will do fine (Area 51). You will see that no finesse was wasted on some of the originals when it came to soldering either! Now, although I have not experienced failures of paired 1N4007 (1kV) diodes in this application (yet), Ron Best, One Thing Audio, Coventry, England, advises that he has seen numerous failures of this particular part in this application over the years. So, to be really safe, and long-term reliable, replace the diodes with either a 3kV (or higher rating) diode for each pair that is in the EHT standard, or, use pairs of 2kV rated diodes to replace those that are in there. The failure of the 1N4007 is more likely at the “top” of the ladder where the voltages are higher.
  7. Spray the completed board with circuit board lacquer (acrylic) or corona dope - pretty much the same thing - but do read the labels.
  8. Place the circuit board back in the small phenolic box. It is a good idea to check the physical integrity of the box, and re-glue the corners if required.
  9. Re-melt the wax, and some spare bees wax, if you have it. (Hint: Saddle makers, and leather workers keep bees wax).
  10. Pour the wax back into the box quickly, so that the bottom layers have no real chance to set before most of the wax is in. Watch it! A hot wax scald is pretty painful - he said - having experienced a few.

OK, that's really about it. Re-fit the EHT block to the mains transformer cage, unless you have that disassembled for work on the neon lamp, or voltage adjustment circuit, or you want to re-spray the cage metal in a tasteful hammer crackle gray.

 This is the part of the Quad Electrostatic that everyone wants to refurbish. Why? It's very likely that they've been naughty, or someone has, and run the thing to death by arcing it. In fairness to those (including me) who've arced a treble panel, it has to be said that as the panels get older the efficiency declines for a variety of reasons, including loss of tension in the diaphragms, and loss of coating. The efficiency loss is about 15% over the first 5 years, and after that the decline is slower with a plateau of about 70% of factory original efficiency after 10 years. {Many thanks to Ron Best of One Thing - Audio, Coventry, U.K. for this data on panel efficiency.} We have this phenomenon sneak up on us, and then one day - poof - lightning strikes!

Arced panels can go on working reasonably well, in fact, provided that the arc point was not near one of the EHT pickup rivets that enter the panel. In that case, the diaphragm will probably not charge very well, if at all, resulting in significant loss of efficiency, or no sound at all!

The original panel diaphragms were made from 6 mm tensilised Mylar® which is not made any more by DuPont. Other tensilised 6 mm polyesters are available - Skyrol® - for one, and if you are prepared to buy 8 tonnes of it, SKC will run it off for you right away sir. Personally, I don't think I could afford the postage on that. We have made-to-original-spec 6-micron tensilised P.E.T. film available in Area 51 of this site.

The materials mentioned above are probably the best ever made for the diaphragms of electrostatic speakers. Quad Electroacoustics use a 3.5 mm
Melinex ® in the new Quad 988 and 989, but I think that working with a film this fine for the DIY refurbisher would be more than a little tricky.

Many refurbishers use 12 mm Mylar® and use a higher diaphragm tension. The results are very good, although tensioning the diaphragm may be more critical to keep the resonance in the supersonic region. Getting the resonance in the supersonic region is a piece of cake with 6 mm material which has a resonance, when properly (and lightly) tensioned at 28kHz - 32kHz. If your diaphragm tension is too low the panel will buzz or make flapping noises like a stack paper being shuffled.

One caveat with these notes is that I am not providing as many pictures as for bass panel reconstruction, since the panel construction is pretty much identical, except for a few details that I will call out in the notes as we go along. For the sake of some completeness, though, here is a picture of a disassembled treble panel. You can see much more detail in the (larger) bass panel pictures, if the structure is not clear enough here.

Materials List:

o Fine Sand Paper (600 grit and finer)
o Silver Loaded Paint
o Gray Enamel Paint
o High Voltage Wire
o Solder & Soldering Iron(s)
o Dust Cover Shrink Film (12 mm or less in thickness)
o PVC Tape (2")
o Aluminium Tape/Foil
o Mylar® or other suitable 6 mm or 12 mm polyester film
o Isopropyl Alcohol and/or Acetone
o Corona or Circuit Board Lacquer
o Diaphragm Coating Material (CALATON CB, ELVAMIDE,
                                                     DIY soluble nylon, graphite)
o Screw Drivers (Flat blade & Philips)
o 60 x 12mm x 3mm machine bolts
o 60 x 3mm Hex nuts for bolts
o 120 x 3mm washers for each side of panel
o Hobby Knife
o Masking Tape
o See Parts Section for Suppliers, or Area 51

N.B. I have described a coating method below using graphite, but it is not the best coating to use, by far. Soluble nylon is the original coating, and I believe, the best for this speaker. You can buy soluble nylon in Area 51 on this site, if you wish along with instructions on how to use it and that purchase will also help keep this site on-line.


Stators & Dust Covers

  1. Physically disconnect and remove the panel from the speaker. This procedure is described in the Disassembly Section, and this section should be read, and well understood, before attempting to remove any panels from the speaker. With the panel now removed, you can (almost) see the structure . It is a five layer composite. The two obvious outer layers are the dust covers. The next two (still obvious) layers are the perforated stators. The centremost layer is the diaphragm - not obvious, you cannot see it at this point. The actual treble panel looks like this when disassembled. Fresh out of the speaker it will have the dust covers on front and rear and be held together with clear tape around the perimeter.
  2. Remove the dust covers by carefully slitting the tape around the periphery of the panel and unfastening the four 2mm diameter bolts and the felt washers that penetrate the dust covers and the panel. N.B. Note the position of these items carefully as they must be refitted. Keep a vacuum cleaner handy, you'll generate a lot of dust here with old panels! Be careful not to cut into the stators, they're only plastic; or, indeed, the wooden frames as these are very light wood. Put the dust covers aside for replacement separately. You can now clearly appreciate the physical state of the outside surfaces of panels. There will probably be spots of missing gray paint. The gray paint is just that - gray paint - on the outside. Clean it up and touch it up as you like. Spots of "corrosion" may be evident around the rivets, although this is very much less likely than with bass panels. You can clearly see that the treble panel is held together with about 60 rivets - what a bastard! Why rivets? They are: 1) quick & easy to use, 2) don't present much sharp surface for corona to form, 3) are cheap and 4) allow a close fitting dust cover. They are also a complete bastard to remove!
  3. Remove the rivets holding the two stators together. This can be done by crimping the rivets in two directions at 90o to each other and pushing the rivet out. I use a high speed drill, like an Arlec Super Tooltm. A fair bit of heat is generated, and the stator will often soften slightly. I view this as somewhat of an advantage, if you don't overdo it(!). The rivet will push easily out through the original hole after a couple of seconds drilling with the appropriate abrasive head on the tool. I use a 3.5mm carborundum ball. The hole will be slightly enlarged, but this is not a problem, since we re-fasten with 3mm bolts and nuts, with washers. This operation is a pain in the bum, takes a long time, generates a lot of dust and dirt, and you need to clean the whole of each stator when finished, whichever method you use. Try not to knock off any more of the paint on the outside. If any red plastic is showing, then you will only need to re-coat with gray paint, for cosmetic purposes.
  4. Once the rivets are removed, remove the two small bolts that attach the EHT line (thin red wire) to panel and then you can separate the two stators. The stators are not glued together, but they may separate reluctantly because they've been squeezed together in there for a lot of years. Use a fine blade screwdriver if necessary to gently prise them apart. The diaphragm is only attached to one of the stators. The diaphragm , if it is original, will have white, streaky marks all over it. This is a CALATON® coating used by Quad at the factory. The diaphragm can be removed, since you have decided to replace it.
  5. Carefully scrape off, or sand off, any remaining diaphragm material and glue at the edges of the stators. Use a fine paper, about 600 grit wet & dry is OK. Try not to make any deep scratches - anywhere!
  6. Thoroughly vacuum clean the stators so that all dust, paint, et cetera, is removed. You should now have a clean treble stator, with perhaps an obvious spot on the inside in one of the "wells" where the panel has arced and the gray paint and the conductive coating on the inside have been burned off.
  7. Examine the stator structure thoroughly. A normal stator looks like a smaller copy of the bass panel. The aluminium tape around the edges seems to be missing and the carbon tracks on the two centre “ribs” seem to be missing. The ribs in towards the centre and the ribs at the edges of the stator have strips of what looks like masking tape running down the length of the rib. They cover gray paint, and under the paint - carbon tracks. The wax paper is there to damp the membrane at the much higher frequencies that this panel works at. The paper is not needed in the lower frequency bass panels. So, there is the mystery of how the 'treble panel gets its charge - solved. It gets its charge from the two EHT bolts which contact the carbon 'frame' the same as in the bass panel. It is just that in the treble panel these have been covered by gray paint and the paper strips. { Many thanks to Ron Best of One Thing Audio, Coventry, U.K., for his information on this point. I was confused about it for years. }
  8. Clean any arced areas with fine (600 grit) sand paper. You may have to take badly arced areas right back to the red plastic base material. Do not remove more than is necessary and then clean carefully with mild soap and water or isopropyl alcohol. Isopropyl alcohol is not aggressive on this type of plastic. DO NOT USE ACETONE.
  9. Paint the area that you have just cleaned down with conductive paint. Silver loaded paint is best (and most expensive), but other types, such as those used to repair windscreen heater tracks also work. Be careful that none of this 'drools' into the perforations. Even really bad areas of arcing can be coated easily and quickly with dabs from a small artists brush.
  10. When the conductive paint is dry - usually about 5 minutes, or less - you can cover the conductive layer with gray paint. A spray of corona lacquer or Circuit Board lacquer won't hurt once the gray paint is dry, and will slightly decrease the risk of future arcing..
  11. Once all arced areas are repaired as noted above, you only need to ensure that the panel is cosmetically acceptable, and that the strips of 'masking tape' are OK. These strips damp standing waves in the membrane and are not there for decoration, so if you damaged them, replace them.


Diaphragm Replacement

OK, you've got this far, and you're feeling pretty pleased with yourself. Let's see what we can do about that, then!! By this stage you should have two clean, repaired stators, with no arced spots or conductive layer discontinuities.

  1. Cut a piece of 12 mm Mylar® (or 6mm P.E.T.®) which is about 10 cm larger than the treble panel stator in each dimension.
  2. Clean a smooth laminex or glass topped table with ordinary household detergent. Dry well, and then clean with either isopropyl alcohol or acetone. N.B. Both of these materials are flammable. Acetone in particular!! Do not allow anyone to smoke or bring a naked flame into the same HOUSE with acetone. Both materials are relatively innocuous, otherwise. Your objective here is to remove anything of a lumpy, or gritty nature from the work area.
  3. Lay out the diaphragm film smoothly on the table top, and fix the corners with masking tape, stretching the film slightly as you do this. Then attach masking tape to the centres of each side, stretching the Mylar ® again, in each direction. Continue taping each side by "splitting the difference" between previous tape points, until you have the Mylar® reasonably taught. Don't try to get it very tight at this point, but do tape it firmly all around.
  4. Using the inner stator dimensions as a guide, mark, or mask off, a rectangle to be coated.
  5. If using graphite, rub the powdered graphite into the Mylar® as hard as you can without tearing it (of course). Try to really grind it in, and get a uniform coating. Test the surface for uniform conductivity with a surface resistivity meter or DVM that can read to at least 100 MW. This will produce a diaphragm which is far too low in resistance to be really useful in a Quad Electrostatic. Don't panic!! N.B. Soluble NYLON is the best coating to use, and it just wipes on in alcohol solution.
  6. Try to rub off all the graphite, using a paper towel soaked in isopropyl alcohol. A graphite glaze will be produced, and the colour of the diaphragm will appear a very light gray. Do try to rub off all the graphite. IF you ground it into the film well enough, it won't come off completely.
  7. Check the resistance with your meter. If it is not at least 100 MW then try rubbing the graphite off a little more. You also need to avoid making large discontinuities in the membrane coating. This is why this method is such a pain, even if the process is, practically speaking, very simple. When the membrane measures as you would like it, clean the general surroundings, but leave the Mylar® taped to the table top.
  8. If you want to avoid this rubbing and grunting and carrying on, just wipe on some DIY soluble nylon, or CALATON CB or ELVAMIDE any of which will duplicate the original Quad diaphragm coating, and wait for it to dry off. Diaphragm coated - no effort.
  9. Mix up some two part epoxy resin glue - the PLAIN kind - no metal fillers!!
  10. Choose a stator to glue the membrane to.
  11. Apply a thin (1/8th inch) bead around the perimeter where the old brown (factory) glue was. Do not put epoxy on the tapes at the edges. The bead should be run between the tape and the outer edge of the stator plastic.
  12. Place the stator, glue side down(!) over the Mylar® film being very, very careful to align the inner rectangle of the stator with the coated area. If you mark up the position accurately with a felt pen, this is not a real problem - just plan ahead.
  13. Press down with both thumbs all around the perimeter of the stator where the bead of glue was run. The idea is to squeeze the glue into a very thin film. N.B. Placing weights on the stator at this time, alone, will not do a good enough job.
  14. Place a layer of books, a sheet of steel, or something solid, over the stator to spread the pressure, and weight the whole thing with bricks. Wait until the glue is well cured. I leave the stator overnight, usually, no matter which epoxy I use.
  15. When the glue is well cured, remove all the weights and other paraphernalia, and lift up the stator with diaphragm attached. Trim the edges very carefully with a very sharp knife, (e.g. Stanley Knife).
  16. Heat Shrink the diaphragm with a heat gun set at about 400 Watts, working about 20 to 30 cm from the diaphragm. There are so many variables involved in this, that it is impossible to give precise instructions. If you have not done this before, then you must practice with a spare piece of Mylar®. Tape a 20cm x 20cm piece of Mylar® film to a table top and practice heat shrinking until you can shrink the film tightly (no little creases) without melting a hole in the film! If you melt a hole in the diaphragm, then you can start again.
  17. Coat the exposed side of the diaphragm with DIY soluble Nylon if you are using the original coating. This is what Quad did at the factory, and what you should do if you want the speaker restored to its original condition. See the FAQs for an explanation of why this is so.
  18. Melt holes in the diaphragm for each stator hole (~60 holes) with a fine-pointed tip on a small wattage soldering iron.
  19. Double check that the heat shrink job is OK. If not, carefully heat shrink again. Leave overnight and repeat the heat shrinking if not sure. The diaphragm should be perfectly smooth, for treble panels.
  20. Using 9mm x 3mm (M3) bolts, hex nuts, and two washers (one each side), bolt the stators together. Tighten each nut and bolt firmly, but not too tight.
  21. Take the refurbished Dust Covers and identify the rear cover. This will need new, large holes drilled in it to accommodate the hex nuts on the rear stator. Otherwise the panel, overall, will be thicker than the original and will not fit into the frame without other unpleasant maneuvering.
  22. Re-fit the dust covers such that the signal leads (brown and blue) and the EHT lead (red) exit through the side. There's a couple of small checks in the timber frame, so this is not hard to identify and do. Tape all around with PVC tape to seal and insulate, but don't overdo it. Thick layers of tape will make it hard to fit the panel into place in the speaker frame.
  23. I recommend fitting the dust cover film such that is glued reasonably tight and free of wrinkles, as far as possible by hand. Then, when both covers are re-fitted to the panel I heat shrink both at that time.
  24. Melt four (4) holes in the dust cover film where the four small bolts and felt washers were originally located. Re-fitting of these felt washers is essential as they prevent the dust cover from rattling and buzzing at high frequencies.
  25. The panel is now ready to be refitted to the frame and the appropriate solder connections to the EHT and Audio transformer can be made now or later. When re-wiring to the audio transformer, make sure that FRONT and BACK connections for the brown and blue wires are strictly observed, or you will have one part of the panel running out of phase with another part of the panel or the bass panels, or both.