Power Filtering vs Power Regeneration?

Halcro,
Have you actually documented what's going on at the wall socket during those periods where the sound deteriorates? It would first be prudent to do that, so you are not wasting money on a (expensive) power regenerator. Another reason to do that is to determine the magnitude of the AC voltage swings, if indeed that is the cause of your problem. Because different regenerators will have different capacity to maintain constant AC output for a given variation in input AC. Two excellent brands of regenerator: PS Audio and Furman.

It's also possible that someone in your neighborhood who shares your AC or some household appliance is switching in and out, causing disturbance on your AC line, when switched in. In that case, of course, you need some sort of filter or dedicated AC lines, or both, and not necessarily a regenerator.

Pani, A passive device simply cannot solve Halcro's problem, if the problem has to do with AC power sags or surges. End of story.

Halcro, If you search on eBay you may find an inexpensive chart recorder that can be used to monitor AC at the wall socket vs time. What is the wattage rating of the P3? Can it handle your amplifiers' peak needs? That's the big issue with using a power regenerator to supply an amplifier. Otherwise, good choice.
I use a PS Audio 300 (300W) to supply the front end of my basement Beveridge-based system. After 10 minutes, I would not live without it, just for its cleansing effect on the music. (I of course do not use it to power the Beveridge direct-drive amplifiers; they just plug directly into the wall.)

Tony, Can you say what "tube gear" would be more affected by humidity than SS gear? I don't think so.

The symptoms Henry describes do not at all sound like anything that can be caused by poor grounding. RF, maybe. Henry, what did your PS Audio do when the wall voltage varied up and down? Did you notice any change in sound quality? If it happens again, you may try momentarily bypassing your PS Audio, in order to determine whether AC voltage instability might in fact be causative. If you are close to a power station, there may be very high voltage lines somewhere near your house; those can certainly radiate RF garbage.

Tony, It is most likely that your friend's system was affected by humidity because of the sensitivity of ESL speakers, especially Quads, to humidity. Humidity affects the tension of the mylar diaphragm, AND it also affects the static charge in the space between the diaphragm and the stators. As I recall, Sound Labs have had a lot of problems shipping their ESLs to customers in the South Pacific, e.g., the Phillipines and Malaysia, for this reason. Thankfully, those of us residing in sealed, heated, and air conditioned dwellings in the temperate parts of the US have only minor problems with ESLs. ESLs are also temperamental at high altitude and in excessively dry air.