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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

Contact Details:


Classique House,
61 Aylestone Drive,
(0116) 2835821
Web Site : OneThingAudio




Clamp Boards

£29-50 each

Hi-Spec Rectifier Board (RBT2)

£50-00 each

'303' treble Protection board

£12-00 each

Dust Cover Material, Kit.


OTEC Treble Panel


Original Bass Panel Rebuild


Rebuilt and Tested Treble Panel

£ 90-00

High Spec Audio Transformer (exchange price)

£ 60-00

Audio Transformer mod & Upgrade Kit.

£ 35-00 pair

AC Bulgin Plug (round) - new stock

£ 4-95 each

The 'Butterworth' Heavy Duty stand (Light Oak only)

£ 399-00 pair

Loudspeaker stands (very attractive!) The 'Rupert' finishes: Ebony, Light Oak or Mahogany

£ 175-00 pair

Standard service/refurbishment ESL 57 (Reviewed Hi-Fi World, April 1999)

£ 375-00 pair

Stocking Black/Midnight Blue/Brown incl. Fitting

£ 60-00 pair

Total rebuild (refurbishment/all panels & components)

£ 1 000-00 pair




Panel Rebuild (any type)

£ 100-00

Input R/C Upgrade Kit

£ 75-00

STD1 Spark Detector Board & Zener Clamp (per pair only)

£ 100-00

Stockings (Black/Brown)

£ 38-00 pair

Dust cover material complete kit

£ 20-00

The 'George' speaker stands: Ebony/Light Oak/Mahogany

£ 175-00

The 'Brooke' heavy Duty stand (Light Oak only)

£ 399-00

One Thing Multiplex decoder Mk 3 (Reviewed Hi-Fi World, June 1999)

£ 175-00


OT High Resolution Speaker Cables


3 metres (per pair)

£ 80-00

5 metres (per pair)

£ 120-00

7 metres (per pair)

£ 160-00


OT silver-plated RFI suppressed & voltage surge protected mains cable


1.5 metres

£ 60-00

Longer lengths to order by quotation.






Contact Details:


QUAD Musikwiedergabe GmbH Brunnenstrasse 57 56751 Gering (German Highlands) Germany



Tel:  +49 2654987977






e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.



Current Part Prices are shown on the web site listed above.


All material below is from an old Quad service manual, and is not intended to be highly informational to the novice refurbisher.



Circuit Diagram (click for full image)

As shown in the photograph, the Quad Electrostatic Loudspeaker consists of five major components:

· Two Bass Panels

· One Treble Panel

· An Audio Transformer

· An EHT Supply Unit.

If any repairs are necessary, it should be determined which of the five components is the cause of the fault, and the component should be replaced or repaired as appropriate.

The following notes may assist diagnosis of faults:

Loss of Sensitivity

Check the EHT voltage, which should be: Bass 6kV +/- 7%; Treble 1.5kV +/- 7%. If low, check, by disconnecting, whether due to leakage in speaker unit or fault within EHT unit. Voltages must be checked only with electrostatic meters, as the current drain from other types may damage the rectifiers.


  1. Make sure that the speaker is really at fault by comparison with a second electrostatic speaker, using a Quad amplifier.
  2. Check EHT voltage
  3. Suspect intermittent breakdown in speaker units.
  4. Suspect intermittent breakdown in audio transformer unit. (Note: a fault in this unit is very unlikely).

No Output at All

Suspect EHT unit or audio transformer unit after checking more obvious things like external connections, not forgetting the leads under the transformer unit connecting the input sockets.

Background Noise

One cause of background noise in the electrostatic loudspeaker is internal discharge of the EHT supply at times of high humidity, or high voltage, or both. This may be reduced by lowering the EHT voltage and a tap is provided on the EHT mains transformer for this purpose. The connections to the EHT rectifier block are normally taken from tags marked Common and 610V. The latter is the right-hand end tag and next to it is a blank tag marked 590V to which should be transferred the lead normally connected to the 610V tag.

Before the EHT unit is touched the mains should be completely disconnected and the loudspeaker left to stand for two hours to ensure it is completely discharged.

Background noise may also be caused by discharge of the EHT from points external to the loudspeaker units, at the tags on the rectifier block for example, if a hair of felt or piece of fluff comes in reasonably close proximity to that point, or if a spike of solder or sharp point of wire permits corona discharge. Where EHT leakage occurs via a bass unit, this is sometimes found to be discharging from one of the eyelets around the periphery of the bass unit plates, probably to one of the aluminium brackets. In such cases a satisfactory repair can be effected by slitting the polythene tape round the edges of the unit, opening the dust cover frames and insulating the leak by applying a single layer of similar polythene tape all round the periphery of the internal plates, on top of the existing sealing tape, and reassembling the dust covers, again with polythene tape. Other internal failures of insulation will probably necessitate replacing the loudspeaker unit affected.

Mechanical If the dust seal covers should be torn, it may be necessary to replace the complete unit as there will have been ingress of dust, which causes loss of sensitivity of the unit concerned.



The loudspeaker should be switched off for about two hours before the grilles are removed, so as to ensure the EHT unit has completely discharged.

The component loudspeaker units of the QUAD electrostatic loudspeaker must be handled with the utmost care partly because when not supported by the rigid frame of the cabinet they are more liable to physical distortion which would reduce the small internal clearances, and partly because the dust covers are necessarily made of very thin and therefore fragile plastic film. At the rear of the treble unit are four pins, located in the wooden struts of the cabinet, and as these represent an additional hazard to the dust covers of the treble unit, the positioning of this unit requires particular care. Soldered joints should be smoothed and rounded and all spikes of solder, wisps of wire, etc., removed as these would tend to cause arcing at the high internal voltages used.

Removing Front and Rear Expanded Metal Grilles

The rear grille is held only by the screws around its periphery. For the front grille it is necessary first to remove the side mouldings, the staples through the metal beneath them, and the screws under the baseboard. Then the bottom edge of the grille is lifted gently outwards and upwards until the top rear edge may be slipped out of its groove in the cabinet, when the whole grille will be free. Care must be taken not to strain the top curved section during removal or the metal may split.

Replacing the Front Grille

Replacement grilles are normally supplied cut and pre-formed so the procedure is as for refitting an existing grille. It may be found helpful when working single handed, having inserted the top back edge of the sheet into the slot in the cabinet, to hold the bottom edge of the grille under slight tension to the bottom of the wooden frame by means of elastic bands and simple hooks of wire, such as an opened paper clip, and then to use a bar of wood slightly longer than the width of the sheet, and with a good flat face, to bed the grille to the frame by moving the bar progressively down the face of the grille, tacking the sides as you go, finally securing the bottom edge with the screws removed from the old grille. Do not forget to fasten the earthing lead to the grille.

Replacing Bass and Treble Units

  1. Remove both grilles.
  2. Remove the top and bottom aluminium brackets in front of the centre (treble) unit.
  3. If the treble unit is to be replaced, it should now be disconnected from the audio transformer (the large rectangular can on the left-hand side when viewed from the rear). This is held in position solely by four screws whose heads are accessible below the baseboard of the speaker. If the speaker is tilted to provide access to slacken these screws it must be restored to its upright position before they are removed or the transformer will have no support other than its connecting wires.
  4. Carefully prise out one bass unit and slide it past the front of the treble unit until the outer edge clears the remaining bracket at top and bottom of the cabinet.
  5. Either disconnect and remove the bass unit if this has to be replaced or move it far enough to enable access to be obtained to the treble unit, as required. To remove the treble unit ensure it is free of the four pins mentioned on page 3, then slide it sideways into the space vacated by the bass unit already moved and lift it out.

EHT and Audio Transformer Units

Only the rear grille need be removed to provide access to these units. Both are secured by screws through the base board only and if the speaker is tilted to obtain access to these screw heads it must be restored to the upright position before the screws are removed or the unit will have no support other than its connecting wires. Place a sheet of cardboard behind the EHT unit to protect the thin plastic dust cover of the bass unit from accidental damage due to specks or solder of wire ends. Etc. Note and mark the flexible connections to the rectifier block so as to ensure correct reconnection.


To replace the rectifier block of the EHT unit, undo the two 4BA nuts securing it to the framework of the EHT unit and remove it. If the replacement block is found to be of a different type it will still be electrically and physically interchangeable with the earlier type, and the equivalent connections are shown in Fig. 1. If the leads to the loudspeaker units have to be extended, the joints should be insulated with high voltage sleeving and staggered so that two joints do not lie together.

Reassembling the Speaker

To reassemble, the dismantling procedure is reversed, but in addition it will be necessary to remove any wrinkles which may have appeared in the treble unit's front and rear dust covers, as these will produce audible rattles when the speaker is in use. This is achieved by means of gentle heat which thermosets the plastic film, and may most conveniently be applied by means of a small warm air blower, such as a hand-held dryer. The nozzle should be held about 18 from the dust cover and moved up and down the unit as uniformly as possible at a speed of about 3" per second, in regular lines so as to cover the whole area. Repeat until all wrinkles have disappeared, but always treat the whole area and do not tackle individual wrinkles separately.

A certain amount of skill is required in this operation. Obviously if the nozzle is not close enough and/or the speed of travel too great, there will not be enough heat to affect the cover. On the other hand too much heat at one point can quickly burn a hole. When carrying out this process for the first time, progressively reduce the distance and speed until the desired results are obtained.

Heat should not be applied to the bass unit covers. Any slight wrinkles in these covers will rarely have any audible effect and will in any case normally disappear as the tensions even themselves out in a few days. After thermosetting the treble unit dust covers, the damping felts behind the treble unit must be stretched and fixed so that there is no contact between them and the treble dust cover, as this will also affect reproduction.

Fitting New Dust Covers

Note: The plates and dust cover material acquire a static charge and if placed in a dusty atmosphere or near any accumulation of dust it will adhere to them, with deleterious effects. Only plastic film supplied by Acoustical should be used. Specify whether for bass or treble unit when ordering.

First remove the faulty unit from speaker as described on page 4, and strip the adhesive tape from around its edges to release the two dust cover frames. On bass units carefully disconnect the three wires from the terminal board, having noted their positions, and remove the board. Clean all loose dust cover material from the wooden frames since any pieces left to flap will buzz.

Spread enough of the new dust cover material on to any clean, solid, flat surface to leave about 6" surplus all around the frame, and hold in position with pieces of adhesive tape at each corner and at intervals along the sides as required.

The materials should not be over stretched but just tightly enough to remove the wrinkles.

Adhesive can now be applied to the frame, the frame placed into position on the material and left to dry. The adhesive should preferably be of a type which does not set brittle, such as Samual Jones' Samson C203, Evostick, etc. When this is dry, use a razor blade to trim off all surplus cover material back to the edge of the frame. The holes to the terminals should be BURNT through the film with a small soldering iron. If pierced cold the material will in time split and run the whole length of the dust cover.

When a pair of covers have been made, the unit and the covers should be blown with a jet of dry air to remove any dust particles etc., which have adhered to them, as this will cause a loss in sensitivity.

GREAT care should be taken if it is found necessary to renew any soldered joints on the plates. Anything more than a quick touch to the tags will soften the plate material and loosen the solder tag. A heat sink is helpful here.

When reconnecting to the terminals be sure not to cross wires as this will result in the failure of the speaker to work.

The unit should be replaced between the two frames and sealed with 2~ wide polythene adhesive tape all around the outside edge of the frames as before.

This completes the recovering and the unit can now be reassembled into position in the speaker.


At serial number 16800 (March 1966) additional filtering was added to protect the treble unit from damage due to high level low frequency signals. Earlier speakers may be modified as described below, when they are to be used with the Quad 303 or other suitable amplifiers of comparable output.

The components required can be obtained ready assembled on a tag board, if required, and Fig. 2 shows this in position under the audio transformer. Alternatively, suitable resistors and capacitors from normal servicing stocks, may be used if preferred.

The above figure shows the tag board layout from serial number 16800 onwards. Modifications to loudspeakers earlier than serial number 16800 when used with the Quad 303 amplifier.

  • Remove the mains supply from the speaker and allow two hours for the EHT to discharge.
  • Undo the screws all around the periphery of the rear grille and remove the grille.
  • Tilt the loudspeaker to permit access to the underside of the baseboard. taking care not to dent the front grille.
  • Remove the four screws holding the audio transformer (large can on the left hand side) in place, remembering to support the transformer before it is freed or it may slip and damage the left hand bass unit dust cover.
  • Restore the speaker to an upright position and invert the audio transformer, taking care not to strain its external wiring.
  • Remove the two drive screws on the right-hand side of the tag board and use these to secure the small tag board supplied, as shown in Fig. 2.
  • Rewire as shown, ensuring that the brown lead which has to be stretched to reach its new anchor point does not press against any sharp edges of turret lugs or solder.
  • Re-assemble the speaker in the reverse order of operations 1 to 5.


If you have bought the speaker second hand, or you are in the process of doing so(!), it is only prudent to inspect the outside first. Look for the obvious - scratches and dents on the front grilles. I have seen everything from pristine, better-than-showroom-perfect to serious cracks in the front grille. This damage is not to be taken lightly, check out the price of a new front grille in the Parts Section of this site, if you need motivating!

By the bye, there are only two “original” colours - black, and “bronze/gold”. The black finish is satin, not matt, on the grille and the wooden framework. White is produced in Germany, and is non-original, but very nice and every bit as good. Other colours? They've been re-sprayed by the owner(s) over the years. If someone has re-sprayed it, check that they didn't clog up the smaller grille openings with too much paint. Look at the back of the speaker. If it is in original condition (more or less) then you will see that the back of the speaker is covered in a diagonal pattern mesh that has a jute fibre mat glued to the inside of the mesh with bitumen - exactly that in the oldest speakers. It's black, it's icky, and it's there, if the speaker hasn't been fiddled with too much. Looking under the bottom of this stuff or around the side of it you may be able to see the dust covers with a torch and look for splits, cracks and such. Otherwise, you need its clothes off!

Look at the wooden side rails. The standard side rail is a light brown, clear finish in the shape of a thin, elongated banana (what can I say?). It is held to the sides with three bronze coloured wood screws. The screws have a nicely recessed washer each. I have seen non-standard side rails fitted, and the screws used to affix them were too long, drilling into the sides of the bass panels - ouch! Again, if these rails are knocked about, scratched and dented, then ask for a bit more off the price if you think its a bit high. See the Parts Section for the price of side rails!

Grilles Off...

  1. The wooden side rails are removed by removing the three screws holding them on. You will then see that the grilles are stapled to the sides with standard industrial wood staples.
  2. Remove the staples holding down the side of the grille carefully (its only aluminium) with pliers and a screwdriver.
  3. Place the speaker carefully on its back.
  4. Remove the line of 10 or 11 small (1/2 inch) wood screws that should be holding the bottom of the grille onto the frame. This completes removal of all standard, factory-fitted fasteners. Do a quick inspection for anything 'non-standard' before proceeding though.
  5. The grille is removed by very carefully lifting it out and upwards in a gentle arc from the bottom. The top of the grille is folded such that it engages a slot in the top, back of the frame. The grille must be removed so that this fold and overall curvature of the grille is not distorted to any extent. If you bend the grille badly, you'll never get it back together again properly.

Dust Covers and Panels...

You are now in a position, literally, to inspect the dust covers, and the treble panel in particular. You may not be able to visually inspect the bass panels at this point since the factory sprayed them with gray paint. Inspection of the dust covers should reveal quite a bit of dust(!), if the owner has never had the grilles off. This is easily removed with a gentle wipe with a cloth that has been soaked in detergent and water, and then wrung out to be mildly damp. We don't want a lot of water in the speaker whether it's on or off! Any splits and tears in the front dust covers will now be obvious, as will repairs to same. They are usually repaired with a little sticky cello tape, or similar thin tape. PVC tape is not suitable. If the dust covers feel brittle when you clean them, and there's a few repairs already, then you need to think seriously about replacing them altogether.

Here is the state of a typical, older dust cover (20 Y.O.) showing some dirt, and simple repairs.



The speaker shown above had a lot of black dirt accumulated around each bass panel rivet, and a clear film repair (bottom right) where the perforated bass stator shows through. It also had treble panel damage which is not clearly visible in this picture.

However, at this point look closely at the treble panel (in the centre). Look carefully into every perforation for carbon spotting. If you see any, then the panel has very likely been overdriven, and arced, causing burning and consequent carbon residue. Sometimes, these 'spots' can be as large as a twenty cent (Aus) piece, or about 25 to 30mm in diameter! In such a case, the treble panel may still even be functioning, if the burn out occurred far from the EHT pick up bolts, but it will not be functioning at optimum, as you can understand. It will, in this case, probably need repairing.


Now that you've given the front a good look over, go around the back of the speaker. The diamond mesh grille and accompanying 'rugs' of jute is held in place by about 18 to 20 small wood screws and some small washers. These are clearly visible around the periphery of the rear frame. Remove them with a flat blade screwdriver. The rear grille is easily maneuvered out, but watch those edges(!), they'll cut you like a knife. In my opinion this is one of the most dangerous parts of disassembling a Quad, never mind the high voltages. Be very careful that you don't puncture the rear dust covers while removing this grille.

Now you will be able to see something like this:



As you can see the treble panel has even more of that felt stuff attached to the rear of the dust cover frame. To inspect the treble panel from the rear you need to carefully remove the felt with pliers and screwdriver. You will then be able to see any arcing (carbon spots) that were not visible from the front. Big arc spots will be easily visible from both sides!

Inspect the rear of the dust covers of each bass panel for splits, old repairs, et cetera. You can also take a close look at the three terminals at the back of each bass panel. The state of the heat shrink tube there will tell you if anyone has previously worked on the speaker.



You've just undressed your first Quad Electrostatic. If you found no damage to the treble or bass panels, or the dust covers, then this is a big plus. We're not out of the woods yet, though. If the speaker still doesn't play very well, seems to lack sensitivity, or if it is very old (most of them) and the EHT block appears untouched, then you will have to re-furbish the EHT block.That's it there, on the right of the photo, sitting on top of the mains transformer cage.