Re: Electrolytics - I have no idea! Besides, I wouldn't know what an electrolytic was if it jumped up and bit me!
OK Bill, you asked for it!
Electrolytic capacitors are the can type, usually with 2 leads coming out of one end. They usually have a liquid electrolyte inside, hence the name. Over time and due to internal heat the electrolyte wears out, and the cap can start to swell and leak. If the goo hits something hot, it smokes and stinks - This is the classic "letting the blue smoke" out joke. That dimple around the waist of an electrolytic gives it away, that seals in the goo. Films don't have a dimple.
Electrolytic Caps
The opposite is a film capacitor which is dry inside, no electrolyte, just layers of conductor and thin insulator wound together. It is much larger for equal capacitance, and less susceptible to change in capacitance and ESR over time, lower leakage current makes them sound better, but they usually cost a lot more.
Film Caps
Note there is no polarity arrow on the films labels. Installing an electrolytic cap backwards makes it overheat and fail, so you will almost always see an arrow stripe on the side of an electro to indicate the negative terminal. Some electros are bipolar however. Films don't care about polarity, (unless you ask an audiophile.) All of the sexy caps people talk about here are film caps. Duelund, VCap, teflon, OIMP, Paper in oil, AudioCap, Multicap, Sonicap, polystyrene, polypropylene, polyester, mica, bypass, coupling caps, output caps, etc. Some mfgs even use film caps in the power supply storage.
When we need values of capacitance that are larger than that available from films, or need it in a smaller package than films can provide or when we need ultra low cost even in small values then we choose electrolytics. In hifi gear, they are usually limited to use in the power supply where large "storage" caps smooth ripple in the DC before hitting the amplifier power rails. This ripple actually causes their eventual demise. In your case it would be the "High Voltage Capacitors" that were replaced. Using electrolytic capacitors in the signal path results in a grainy blurred sound. Consumer gear that has electros in the signal path are prime candidates for upgrade to films.
There are some high quality Japanese electros that sound better than some films. coughcoughsolencough