Stewart Penketh Element Repair


From Stewart Penketh in Canada I have received the following information about his Quad ESL element repair hobby.

Some Quad ESL versions at Stewart Penketh's place

Several years ago, when I found out how much it would cost to repair an arced treble panel on a Quad ESL-57, I rebuilt it myself. I then bought several damaged ESL-57's from a local store, rebuilt them, and sold them back to the store. The proprietor began referring Quad ESL owners to me, one of them being a member of the local audio association ("L'Association Montrealaise des Audiophiles"). This resulted in my rebuilding a pair of ESL-57's for one member, and a pair of B&W DM-70 treble panels for another. To date I have built over 65 panels, split about equally between ESL-57 and ESL-63. Repair work initially arose from word of mouth referral, so that most of my clients are in Montreal. The recent reference to me on the "ESL Hotline" has resulted in work for clients in Ontario and Alberta. I presently own four pairs of ESL-57's and two pairs of ESL-63's. One pair of each is an untouched reference, while all others are modified.

My charge to repair an ESL-63 panel would be $300 Cdn (which converts to approximately $200 US), excluding shipping, and presuming that you remove the panel and replace it.  In addition, if you live out of the province, you have the cost of packaging and shipping the speakers, and if you live outside Canada, there may be customs duty to consider. QS&D perform Quad-authorized panel repairs in North America, and their rates (in US  dollars)  are quoted on their website. This will permit you to assess whether my charge is reasonable.

The  film  I use for ESL-63 diaphragms is 3 micron Mylar ("Hostaphan Polyester") purchased from MT Audio Design in Sweden. For ESL-57 treble panels I use 12 micron Mylar, and for ESL-57 bass panels I use Saran. To the best of my knowledge (since Quad does not volunteer information) these are the same materials and the same thicknesses as the film Quad itself uses. For your information, a micron is one millionth of a metre. Thus the ESL-63 diaphragm is one three-thousandth of a centimetre thick.

Diaphragm Coating
The diaphragm coating I use yields a resistivity over 1,000 megOhm, sufficiently high to ensure that the panel can reproduce all frequencies without charge migration.

The original Quad panel is held by seven bolts (three down the centre-line of the panel, and one at each corner) and several spring clips. My panels have about 20 1/2" bolts around the perimeter of the panel.  These are more effective than spring clips (which tend to snap over time), significantly increase the structural rigidity of the panel, and reduce the likelihood of the diaphragm "creeping." Although I have not yet encountered an ESL-63 whose high-voltage supply needs rebuilding, Quad advised me that after about 20 years power supplies may begin to fade, and that their charge for a replacement pair of ESL-63 EHT units is $290 Cdn, plus postage.  Frankly, that is exorbitant, as the components in the EHT unit cost less than $10.  I have rebuilt many ESL-57 EHT units, but have not yet rebuilt an ESL-63 EHT unit.

The  ESL-57  Hotline ("") comments that it has received user advice that my ESL-63 repair work is meticulous. A link on the Quad home page is to a Montreal site Quad Francophone. Select the "livre  d'or" icon, then the "voir  les messages"  icon, and scroll down to the following messages. You needn't understand French to get the drift of what they are saying : -)  a February 27, 2001 posting by Gilles Lepine. He advised the site's administrator (in  French) that I repaired an ESL-63 panel for him, that the panel works excellently, and  strongly recommends my services because I am honest and meticulous and my rates are fair. an  April  18,  2001 posting by Jean-Pierre Levesque. He advised the site's administrator (in French) that I gave him free, generous and effective advice on how to perform his own repairs, and warmly recommends me to anyone contemplating rebuilding an ESL-57.

Performance of Repaired Panels
My ESL-57 and ESL-63 panels seem to have a more extended bass response and a slightly higher sensitivity than a stock Quad panel. "The Electrostatic Loudspeaker Design Cookbook" by Roger Sanders (the designer of Innersound Eros electrostatic speakers), advises that sensitivity is driven by diaphragm tension, and I believe that my tension is somewhat higher than Quad's.

I have speakers which consist of eight ESL-63 panels stacked in two layers of four, yielding two more bass panels than in a Quad-989. The upper four panels function as in a normal ESL-63, while the lower four function as bass panels. Each segment on all of the lower four panels is fed from the outermost delay line of the upper four panels, so that Quad's concentric circle delay line is respected. As a point of reference, one of the two stacked pairs consists of original ESL-63 panels. By contrast, each of the eight panels on the other pair was rebuilt. Listeners tell me that my rebuilt Quads play deeper than the stock Quads, but in other respects are identical. To put this in perspective, Peter Walker (the founder of Quad) said that it is easy to build a single speaker which sounds fantastic. The real difficulty is to employ unskilled labourers to build 100,000 ESL-57 and ESL-63 speakers over a 40-year period, and have each one sound excellent.

Stacked ESL-63 loudspeaker

Additional Information on ESL-57 Repair

Identifying the Problem
The following simple guidelines should help you to work out what your ESL problem is:

Bass Panel
Quad ESL-57 bass panels have their conductive coating on the outside of the panel. Consequently  bass  panels are extremely difficult to arc, and are rarely damaged. If  the  bass  panel  is  not  working,  or  plays extremely quietly, it is probably because the  EHT (high-voltage) rectifier unit is defective. If you want  to have it repaired, send only the EHT unit itself, and not the entire  metal  frame  and transformer assembly. I offer more details about EHT repair and replacement options later on this page. Often, there is corrosion-effluorescence on the panel around the rivet. It is purely on the conductive paint on the surface of the panel, and has no impact on the panel's performance. See more later on this page.

Treble Panel
Quad ESL-57 treble panels have their conductive coating on the inside of the panel. Consequently they are easily arced.
If  the treble panel is not working at all, it is probably badly arced, and requires a rebuild.
If the treble panel works, but there is a buzzing sound : -
  if there are also sparks, then there is arcing damage and the panel requires a rebuild
  if there are no sparks, then the dustcover has probably lost its tension or is torn and must be replaced.

Stacked ESL-57, original ESL-57 and streching frame

Damaged Dustcovers
Unless  they  have  been torn, bass panel dustcovers rarely need to be replaced. However, the dustcover film Quad uses on the treble panel loses its tension over time, and the film eventually sags onto the convex front of the panel, and then buzzes whenever music is played. Quad bass and treble panel dustcovers behave differently because they use different material. To  check  whether  the dustcover is the problem, simply remove the front grill, check the tension of the dustcover,  and play music to determine where the buzzing comes from. At the same time, you'll be able to see whether there are any arc burns on the treble panel. If the problem is just a torn or buzzing dustcover, I suggest you fix it yourself. Unless you are a perfectionist, it's not worth the time and money to send panels to me just to have dustcovers changed.
I  have  seen speakers which had been used with torn dustcovers for long periods of time, and was surprised to find that nonetheless the panels were in excellent
condition. If they are not in a dusty environment, the panels seem to remain quite clean. Even if there is dust accumulation inside the panel, you may be able to remedy it by removing the dustcovers and vacuuming the "naked" panel. Don't worry that you may damage the diaphragm, it's pretty sturdy, and is sufficiently  tensioned that no vacuum cleaner is likely to suck it up against the stator panel and rip it (if you actually do rip it, it's because it was already damaged). Just make  sure that you disconnect the speaker and let it completely discharge, so that any dust stuck on the diaphragm loses its static attraction to the diaphragm and can be sucked off.

Replacing Dustcovers
To replace a dustcover, buy a package of 3M Window Seal Kit from any hardware store. Follow Sheldon Stokes' instructions on Quad ESLPages for disconnecting the treble panel wires from the transformer, and for removing the treble panel from the speaker. Then remove the front and rear dustcovers from the treble panel proper by cutting through the tape around the panel perimeter. Because the tape is over twenty years old, the glue on it has turned to powder, so proceed slowly, avoiding getting dust in the panel. Once the panel is removed, vacuum it carefully to remove any dust that may have escaped, and put it in a clean garbage bag. Remove film, tape, glue and crud from the two dustcover frames, and attach the film from the window seal kit to the frame using the double-sided tape supplied with the film. Make sure the film is evenly tensioned and has no creases, and your new dustcovers should last for another twenty years. Attach the two dustcovers to the panel with duct tape. You have to pierce the dustcover to accommodate four bolts which pass through both the panel and the dustcover. Do not puncture the dustcover, as it may rip. Instead, melt the holes with a fine-tip soldering iron. Re-install, taking care not to puncture the dustcovers against the exposed nail heads on the frame uprights that Quad uses to hold the panel in place. If you work slowly, and if you are neat and precise, you will have an immediate and audible improvement in the performance of your Quads.

If you are not familiar with Quad ESL-57's, bear in mind that the speaker was designed in the mid-1950's to work with 15-watt amplifiers, and has no protective  circuitry. Given this, an amplifier putting out as little as 30 watts  may arc the treble panel. Even the Quad 303 amplifier can arc an ESL-57, although it was designed specifically for it. You will be surprised at how loudly an ESL-57 can play, but take care to play within the speaker's limits. If you do decide to play loudly, do it at night, in darkness, so that you will be able to see if arcing is occuring. At the point of arcing small flashes of blue light come from various points on the treble panel, and the music acquires a rough edge (like a blues harmonica), as if the amplifier is overloading. Turn down the volume, or else you may damage the panel. The speakers play purely right up until the point of arcing, so the transition is abrupt. You can find the speaker's limit by gradually raising the volume until you see the point at which arcing begins. The speaker will probably be damaged if you raise the volume beyond this limit, or if you play near this limit for a long

Occasionally, you will see what appears to be rust on the panels. It is typically on the bass panel only, and in the vicinity of the panel's rivets. My understanding is that this is not rust but rather effluorescence. This is a benign chemical reaction between the rivet, the panel and the paint, which occurs as chemicals leach out of the paint over time. When the speaker is not in service, which is 99% of the time, we have rivet heads, each carrying a 6,000 volt charge, projecting from an uncharged stator panel. I suspect that the charge each rivet is carrying is sufficient, over time, to stimulate a chemical reaction which does not occur elsewhere on the bass panel, or anywhere on the treble panel. Effluorescence has no impact at all on the integrity of the panel itself. The reaction is purely on the surface of the panel, while the panel interior and diaphragm remain in pristine state. I found it impossible to remove the effluorescence from my own panels without causing damage, and so left the panels as they were. Because rivets holding the two stator panels together pierce the charged diaphragm, Quad had to mask both bass and treble stator panels so that there is no conductive paint in the vicinity of any rivet, so as to avoid a short-circuit. Consequently, the area around each rivet is inert as far as producing sound is concerned.

Stacked ESL-57


Complete  speaker rebuild

$1,000 Cdn/$650 US per speaker (replace diaphragms, dustcovers, new EHT unit)

Enquist EHT unit

$200 Cdn/$130 US per unit

Quad replacement EHT unit

$85 Cdn/$56 US per unit

Replace dustcover

$100 Cdn/$65 US per panel

Panel  rebuild

$300  Cdn/$200 US per panel (replace diaphragm and dustcovers)

The cost of shipping a panel within Canada is about $25 Cdn (including $500 Cdn insurance), so that the total cost of a panel repair would be about $350 Cdn. In addition, US clients may have customs duty to consider. Typically, an ESL-57 needs new EHT units and rebuilt treble panels. Bass panels rarely  need rebuilding.  Unless they have been punctured, bass panel dustcovers rarely need to be replaced, whereas treble panel dustcovers typically need replacing, for reasons explained earlier.
Check  out the Sheldon Stokes website Quad ESLPages. He offers a repair service (specifying charges in US dollars for each service) and gives instructions on how to remove and replace panels, and on how to repair them, if you are tempted. In addition, QS&D perform Quad ESL repairs, and their rates (in US dollars) are quoted on their website. To  confirm  that my rates are reasonable, check rates charged by Sheldon Stokes and by QS&D.

I guarantee my work, excluding only arcing damage due to speaker abuse. An ESL-57 is very fragile, and the client must take care to avoid damage when installing a rebuilt panel himself.

EHT Voltages
I also offer rebuilt ESL-57 EHT (high-voltage) supplies. The specified voltage is 1,500 VDC for the treble panel, and 6,000 VDC for the bass panels. Quad high-voltage supplies tend to weaken after about twenty years. Low volume is a sign that the EHT supply is defective. To confirm, you have to test with a high-voltage probe. Take  note  however, that a general-purpose high-voltage probe will not give the correct reading for the bass output of the EHT unit. The reason is that the probe has an impedance of 1 Gigaohm, while an impedance of at least 10 Gigaohm is required if the probe is not to load the circuit. This loading  the circuit is not a problem under normal circumstances, as high voltages are typically associated with currents of  several Amperes or more. Relative to a current  flow of  several  Amperes, the drain of the probe is insignificant. It is only when the current is almost nonexistent (as is the case in an EHT unit), that the current drain of the probe becomes significant, to the point that it even corrupts the reading. In other words, when the probe tries to take a reading of the EHT's voltage output, it does so by demanding a greater current-flow than the EHT unit can deliver, and so actually reduces the voltage it is trying to read. If an Enquist EHT unit gives a reading of 5,400 volts on a standard high-voltage probe and a Quad unit gives a reading of 4,900 volts, that corresponds to a true 6,000 volt output.

Replacement EHT units
I offer EHT units that I rebuilt myself, replacement units purchased from Quad in England, or units from Anders Enquist in Sweden.
Rebuilt original units cost about $120 Cdn per pair. I rebuild them if the client wants, but prefer not to, as the EHT is markedly inferior to the Enquist. I have all the parts needed to rebuild old Quad EHT units except the capacitors, and it would take me about one week to get them, and another week to rebuild them. If the EHT units on your Quads are the epoxy (i.e. not repairable) type, I possess several repairable EHT units. If  your Quads are not the epoxy type and if you are handy with a soldering iron and can read a circuit diagram, you can rebuild your own EHT units. Parts would cost about $40, and rebuild time would be about 4 hours. However, you'll need to invest another half-day just to find the parts; Radio Shack and Future Electronics don't stock 3kV capacitors or 22 Megaohm resistors. Sheldon Stokes' website specifies the parts required, and the steps to take.

I offer brand-new replacement rectifier units from Quad in England for $170 Cdn a pair, which is the same price I pay Quad. Another source of Quad EHT units is QS&D whose price is $125 US (about $200 Cdn), plus shipping.

I also offer the Enquist EHT Supply, top-of-the-line printed circuit boards from Anders Enquist in Sweden, for $200  Cdn/$130 US per unit. If you want to know more about them, go to the Quad page on The ESL Circuit. Scroll down until you find Enquist. A picture of the Enquist EHT supply is found here. Whereas the Quad EHT unit has no current-limiting resistor at its output, the Enquist unit has a 22 Megaohm resistor, which enables the Enquist unit to maintain a higher voltage even when the probe is "loading" it (or when the diaphragm is leaking). This ability of  the Enquist EHT unit to preserve a higher voltage while under load suggests that the Enquist EHT is superior to the Quad  EHT. The Enquist EHT will ensure the charge on the diaphragm is preserved at 6,000  volts, while the Quad EHT will occasionally permit the charge to fall below that, and such a voltage drop would affect speaker performance. With the Enquist EHT, each panel is fed separately, and each panel is completely isolated except for the brief instant that the EHT unit is actually charging it, while  the Quad EHT is not isolated. This too should have audible consequences. In  addition, because  each panel's neon lamp flashes whenever that particular panel is charging, you can see the health of your panels - how well they hold a charge. For your information, the specification of the capacitor used in the Enquist EHT unit is 4,700pF/3kV.  4,700 pF corresponds to 0.0047 uF. The Enquist EHT uses two capacitors on each rung of the "ladder," which means that they can jointly deliver 0.0094 uFarad. The rating that Sheldon Stokes specifies for the single capacitor that the stock Quad EHT uses on each rung of the "ladder" is 0.01 uF/2kV. The Enquist EHT unit attaches to the rectifier frame where the old Quad EHT unit originally went, and is held by 1.5" 4-40 carriage bolts and 1" stand-offs (all of which I supply). You simply solder the two current-feed wires from the step-up transformer, one earth wire, and the three output wires (one to the treble panel, and one each to the bass panels). Take care to put a sheet of cardboard between the speaker panel and the EHT unit when you are installing it. The dustcover (and possibly even the diaphragm) can easily be punctured by a solder splash or a loose wire.

Stacked ESL-57


Decide what needs to be repaired, and which tasks you wish me to perform. If you only wish me to repair an ESL-57 panel,  follow  Sheldon Stokes' instructions on his Quad ESL Pages on opening the speaker and removing and replacing the panel.
If you need ESL-63 repair, I will send instructions on opening the speaker and removing and replacing the panel. You will need wire cutters, a screwdriver and a soldering iron. You will also have to buy a package of Window-Seal kit (cost  about  $10), to replace the speaker's dustcover. Sheldon Stokes' website advises  that  Quad  itself  recommends  3M window-seal kit for dustcovers. If  you  ever send me an item for repair, it is best to send it to my workplace, as  there  is  no-one  at  my  house  during  the  day to receive a package. In addition,  the  mail-room employee is used to getting packages for me, and knows that  they are fragile and valuable. 

Please  ensure  that  you pack the panel very securely, to ensure that it is not damaged in transit. I usually repair a panel in one week, excluding time in transit.

Stewart Penketh 

Stewart Penketh's ESL-63 (Crosby Mod) assembly picture series
Stewart Penketh's ESL-63 repair picture series
Stewart Penketh's ESL-57 repair picture series
Stewart Penketh's instructions on how to make stacked ESL-63s

EMAIL Stewart Penketh



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