New CrossoverCaps Found
A lot of people have asked about ways to change the ceramic caps in the input crossover circuit. Although I do not hear much difference between the ceramic caps and the new polypropylene caps, there is some merit to changing them. I measured my old ceramic caps and they were out of spec. by about 20%. The original ceramic caps have a voltage rating of 5000 volts. The treble panels arc at about 3300 volts. So those caps can have that much voltage across them under certain conditions.
However, if the gas discharge tubes specified here are used to protect the treble panels, the voltage out of the treble winding is clamped at 1500 volts. So the caps in the crossover will see about that amount of voltage across them. While 3000 volt film caps are hard to find, 1600 volt film caps aren't.
I ordered some 1600 volt metalized polypropylene caps from Digikey (P/N P10496 & P10495). I got 0.001 uF and 0.0012 uF caps. I put a 0.001 uF cap in series with a 0.0012 uF cap to make a 560 pF cap. I used a single 0.0012 uF cap in place of the two parallel 560 pF caps.
I only recommend using these caps when the gas discharge tube is installed, if not the treble panel circuit voltage may exceed the cap voltage. The AC voltage (to 60 Hz) is 150% of the 1600 volt DC voltage.
New Diaphragm Coating Found
I have been experimenting with a new diaphragm coating method to make the diaphragms slightly conductive. For true constant charge operation, the diaphragms should have a very high resistance. This is to insure that the charge on the diaphragm doesn't move appreciably in the time of a half cycle of the lowest frequency reproduced. In practice graphite works quite well, especially when combined with a power supply isolating resistor. But graphite can't get as high a resistance as some other methods, and getting panel to panel resistance consistency can be difficult. Ross Walker told me that the original surface conductivity was 10^10 ohms/square. I have been experimenting with Indium Tin Oxide particles (0.5 micron) suspended in a water based polyester resin. This liquid is painted directly onto the mylar. By varying the amount of dissolved solids in the mixture, the surface conductivity can be varied from about 10^4 ohms/square to 10^11 ohms/square. Using this method, very consistent conductivities can be obtained from panel to panel. The finished resin coating based panels, while sounding no different than the graphite ones I've tested, are more like the original units due to the lower conductivity. The dried solution is also impervious to water, and shouldn't suffer any ill effects due to aging. The polyester resin also bonds nicely to the polyester mylar film.
I will be rebuilding panels for customers using this new technique, unless graphite is specified.
Complete Restorations Offered
Due to the increasing interest in a white glove approach to Quad ESL speaker repair, I'm offering a complete rebuild program. your Quad ESL's are completely disassembled, cleaned and rebuilt. I replace all 6 panels with freshly rebuilt and tested ones. I also replace all the dust covers and rebuild both power supplies. I also rewire the entire speaker, and perform any minor cosmetic repairs needed. The cost of this service is currently $1250 for a stereo pair (a savings of over 40% off the cost of the individual parts). Each speaker is tested and burned in, and comes with a one year warranty on defects in workmanship. Substantial discounts on speaker stands and side panels as well as new grilles are available as part of this offer.
Quad Work Resumes
I am doing a limited amount of rebuilding work now, however I am usually swamped with rebuilds. So if you would like panels or complete speaker rebuilds send me some email and I'll let you know when I can fit you in.