Here are some of those questions that are inevitably asked by people nervously hoping that their speakers are really OK, when they are, in fact, broken. Paraphrased for brevity hereunder.

My speaker is humming.  What is causing that?
Bad news, the Extra High Tension Power supply to the treble and bass panels is leaking through the coated diaphragm to the stators of the original Quad ESL, for example.  This requires a panel rebuild.  This is true in almost all cases for all Quad ESL models.  On the other hand, if it’s humming in time to the music, maybe not so bad.   Look, just kidding, they never hum in time. It’s also not humming because it’s bored with your musical taste.

The other possible cause of a hum, in the original Quad ESL (Quad 57), is the use of a diaphragm coating material that is too low in conductivity.   This speaker can only use a specific soluble nylon coating and because the air gaps in this speaker are so small, it will not work properly without that exact coating. If you have gone down this path and still have hum and don’t know how to coat the diaphragm properly, then it’s time to call the expert at Quads Unlimited.

My speaker is ticking. What’s up?
OK, we’ll assume that there is no nefarious device planted in your speaker by terrorists who just don’t like you.  In that case, the “ticking” is caused by a small arc of high voltage electricity between the diaphragm and stator.  This is internal to the panel and is caused by contamination in the panel in 99% of cases. A split in a dust cover, and some dust gets in and that’s it.

One of my speakers is not as loud as the other, why?
Very probably the Extra High Tension (EHT) block has failed in a significant way. The only way to absolutely confirm is to disassemble the speaker and use a probe attached to a DVM to determine the true voltage compared to the proper specification.  If you don’t know what you are doing exactly, then DO NOT do this.  This is an area only for “trained personnel”.  Seriously folks, this can kill you, so leave it to a qualified expert.

What did Quad use as diaphragm material?
Polyethylene Terypthalate in the treble panel and Polyvinyl Chloride in the bass panels.  It was 6 micron and 12 micron respectively.

Can I buy these materials to DIY repair my speaker?
You sure can.  What usually happens is that most amateur repairers get the materials in hand and can’t tension it properly, or coat it properly and try many times to produce a working diaphragm in the speaker.  Their psychologist then tells them to call Quads Unlimited.

I think I saw a purple glow, are my speakers haunted?
You may well have seen “the glow”.  Unlikely that the speaker is haunted, but, you never know. Have you paid the electric bill this month?  It’s a corona discharge from around the rivets or framing materials that hold the high voltage bits in place.  If it’s not excessive, then maybe not much of a problem.  If it is excessive, you will probably also be wondering about that 50/60Hz hum you’re hearing lately.  This will be when the panel, or panels, has started to “leak” too much.  At that point it needs to come to us for repair.

Can Quads Unlimited sell me some new speakers?
No, only Quad can do that, but not a 57 or a 63, as though just don’t make those anymore.  However, we can sell you rebuilt speakers if they’re “on hand”, that will have been rebuilt to a higher spec than the factory ever made.  You need to ask us about that one.  Not always available, you know?

How long will it take to rebuild my speakers?
Like, we understand, dude, you want them back NOW!  So does everyone else, and therein you see our problem.  This is not a mass production, Chinese, Japanese or Korean car factory.  This is as much a craft as it is a science and we process requests in the order we receive them.  This is NOT because we are a bunch of arrogant ass holes.  It’s because we believe that your job, while it is the current work deserves the utmost attention.  Sometimes that means a few minor repairs, but, more often than not, it means a LOT of major shit happening that has to be corrected.  Your speaker may be up to 60 years old, so we don’t want to miss anything, send it back to you and have a fault five minutes later.  This takes time.

How much will it cost to fix or rebuild my speakers?
Pick a number between $200 and $10,000 … we can only tell exactly once we see the speaker, or some fantastic photos plus an accurate description of what’s going on.  Forget the $10,000 unless you want gold plated grilles and that could run into serious money.

More seriously, here is a scenario:

You email us with the bad news that one of your Quad 57s has started to hum.  This means that several things need to be checked.  The EHT block needs to be measured for correct voltage. A visual inspection of the panels with the grilles off, to see if there are any arc burns that can be seen.  Some are horrendous, others, fairly small.  All are bad news and mean a panel rebuild, if you want the speaker to run as designed.

OK, you tell us you want to send the speaker in and have us rebuild the treble panel because you found a black arc spot on it, or, maybe, swap an old for new panel plus rebuild costs.  Fine.  You install the rebuilt panel and the speaker still hums.  That means it wasn’t the treble panel.  Next suspect is the EHT.  You can measure the voltages with a HT probe and a DVM if you know what you’re doing.  You need to disconnect one bass panel and measure, then the other and measure again.  In the process maybe you find one bass panel is “leaky” and the EHT is down on output.  You then need to install new capacitors in the EHT block, probably newer diodes as well…and so on.

This is just one speaker.  Takes you about a month, possibly two, if you’re a beginner.  Yes, really.  I haven’t mentioned that you’ll need to vacuum clean all the dust out and other minor cleaning matters, have I?  You stand a chance of damaging a panel, or the EHT, or yourself, at any stage in the process if you haven’t done this before, even with the best help and instructions.

Like I said, just one speaker and you get it back in good working order.  What next? You run it with the other speaker and they just don’t match!  One sounds louder than the other, probably the refurbished one is louder.  Only solution is to work on the other speaker, even though you originally thought it was OK.

In short, this very simple example outlines why we usually find that old Quad 57s need a full panel and EHT refurbishment.  This will bring them back into full sonic glory.  If you want all the cosmetics of a 40 – 60 year old speaker brought back to “new” condition, then, clearly, that will cost more of the folding stuff.

The only rough guiding principle is, that the older the speakers, the more likely they will need a complete rebuild.  Fixing an isolated problem in a pair of old speakers is a “hiding to nothing” as they used to say in the game of billiards and will almost certainly cost more than refurbishing the pair from the beginning.