This diagram shows the first stage of my intended x-over upgrade and as such is more of a capacitor parts refreshment. I have tried to keep the replacement caps as close as possible to the type they are replacing, avoiding ESR issues when replacing electrolitycs with polyprops etc. The tweeter film cap bundles are to be replaced with single Sonicap Gen1 200vdc film caps (Polyprops). The 4uf Elcap electrolytic used as a shunt in the midrange is to be renewed by an Alcap 50v electrolytic and the 72uf Elcap shunts in the bass section will be Alcap 100v electrolytics. Alcap are supposed to be the closest match tonally to the original Elcaps, I purchased them from Falcon Acoustics who graded the nominal 10% tolerance caps to +/- 2% for the 4uf 50v and +/- 5% for the 72uf 100v items at extra cost. I bought more than required and refined them further by picking the closest values from the bunch. The original 30uf (total) electrolytic in the midrange was a better quality item as it lies in the signal path. This is to be made up of two 15uf 70v 5% Mundorf ECAP's (electrolytic) again I purchased more than required and graded them for best match.
This upgrade will protect the drivers from possibly leaky old caps but not involve changing the original boards, so is easily reversible and can also accept further changes if required. I am hoping the character of the speakers will not be altered by taking this path. The purchased caps have arrived (Sonicaps from USA) and are currently burning in prior to being fitted. I have used Sonicaps several times before in x-overs and know they take a lot of hours before smoothing out and sounding their best. Some say 180 hours but I thought they didn't change noticeably after 150 hours use. Major changes take place at around 70/90 hours so I will give them 96 hours burn prior to fitting and continue the process when installed in the x-overs/speakers. I find they tend to settle within about 8/10 hours when pre-burned this way, initially having a grainy treble which refines after this short period. Burning them in when fitted to the speakers takes for ever unless you run them 24/7 and the difference between virgin and burned caps is very noticeable. There is little point in trying to assess changes till they have settled.
I burn them by attaching several in series to the positive speaker terminal on an amplifier and adding a 15 Ohm ceramic resistor in series on the end of the chain, as a load, before connecting that to the negative terminal. This way you can turn the volume up to a reasonable level and without speakers connected, leave them switched on without disturbing anyone. All of the above is my way of doing things, other people may take a different approach, but it works for me. The caps will be ready to use in a few days and I will be installing them into the x-overs straight away.