ESL-63 Restoration Questions


Paid Member
2005-01-09 2:32 am
Hey all,

Just got a pair of ESL-63 and getting ready to look into problems. nothing but static on one and intermittent popping on another...

Anyway, first things first - looking for an easy way to check bias voltage to stators. I asked around at work to see if anyone had a voltmeter that goes all the way up to 5kv, - no luck (had to deal with all the "what the HELL are you trying to do with that 5kv" questions)

Anyway, I remember doing something similar on my Acoustat interface years ago where 5kvdc bias voltage was around 76vdc on a basic loaded voltmeter, and worked out OK, but not very accurate.

Another idea I had was to just pull interface power off a variac set to 1/5 of 120vac mains (24vac) and see if I get anywhere near 1kvdc at bias out... maybe a bit more accurate than my Accoustat 76vdc method?

BTW - go easy on me boys and squirrels, as I am just a dumb mechanical engineer...
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2009-07-18 8:16 pm
John....If you take one of the acoustat type or any 500meg res...put it on your hot + leg of your any meter put the other end of the res on bias....I think Bolserst said 86-92 volts was 5k..i use 86volts on my 5k bias an it sounds great....good to see you typing...Bolserst well be here sone set us all strate……..

Thanks for your years of help Bolserst...
If you use a proper HV probe, keep in mind that even a high impedance device like an HV probe will load the bias supply, which has an even higher output impedance. In the case of the Acoustat speakers with their 500M-ohm output resistor, typical HV probes will indicate only about 3.5kV when measuring a 5-kV supply. This will depend on the exact impedance of the probe.

Not sure what outfeed resistor your Quad uses, so your results may vary. The point is that in this application, HV probes are best for relative voltage measurements (i.e. comparing two speakers) rather than absolute voltage measurement. The same can be said of the DVM method.
AcoustatAnswerMan is correct the bias supplies in all the quads is quite wimpy, and any high voltage probe will load it and make the read a voltage lower than you would expect.

I use a crappy beckman high voltage probe that has a 1500meg resistor in it. I get 32-35v on a properly functioning 63 HV supply.

However, your issues aren't the high voltage supplies. The static and popping tells me you have plenty of high voltage. You have stator and diaphragm problems in your panels. Rebuild your 8 panels and you will be all set. After the rebuild, replace the 16v 1000uF cap on the clamp boards, and bypass the 220uF bipolar electrolytic with an 8uf film cap and you will be all set.

hope that helps,


2009-10-19 7:47 pm
the bias supplies in all the quads is quite wimpy, and any high voltage probe will load it and make the read a voltage lower than you would expect.

Are ESL 57s worse than ESL-63s in this regard?

If you measure at the multiplier output (before resistor) does accuracy improve or is there still too little current available to handle the probe's impedance?


Paid Member
2005-01-09 2:32 am
Opened one up and found one panel that had torn mylar, all others diaphragms intact. I have some 3 micron and 6 micron mylar somewhere....since I have two pairs of speaker, I was looking to get one set up and running and the other set to be my experimental units...

Anyway, I glued back the loose stators on three of the four panels. I was looking to add a coating of Sodium Laurate or Licron on top of the existing Quad coating which looks to be good.

Any advice on whether to just leave as is or add coating on top? I have a little bit of Licron Crystal left over from another project...

I tested the two lower panels and had no bias leaks (no Neon blinks) and both panels sounding great....almost there

Also, the upper and lower bass panels and upper and lower mid treble panels are same and not mirror images (same connections on same sides), correct? I see some panels called out as Upper mid/treble and lower mid/treble, and see other references that they are identical in every way.
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From top to bottom # 1 and #4 are bass panels and #2 and #3 are the point source half circles that provide the proper dispersion pattern and must be kept together.

Bass panels can be swapped around but not the midrange sections 2 and 3

I would wipe down the coating but adding more coating would not be advised IMO