What do Oil Caps do and how do they effect sound?

Sean is correct, but remember that many speakers produce their best sound by way of voltage, not wattage. Soundlab is a perfect example.

The ultra high rail voltages of tube amps will typically drive this load better than transistors.

For example, some SET Tube amps rated as low as 20 watts run 1,000 volt (or higher) rail voltage and therefore can swing enough drive the big Soundlabs to near 90 DB SPL.

No 20 watt transistor amp I am aware of would work on big Soundlabs. In addition, transistors hate big impedances in bass, reducing power to a fraction of it's textbook rating. Some tube amps actually produce MORE power at 30 ohms than 8 ohms.

In other words, the answer is not always easy to determine by numbers or text. As always, listening is the most important test you can make.

Albert, I'm not sure whether you were being facetious or not? You actually gave a pretty good argument for using the numbers or text.

Point I was making was, published specifications don't tell us the whole story. Many people assume that the quality, power and sound of an amplifier may be determined by what the manufacturer puts into print.

I admit that some statistics are laughable, but that is not what I was referring to.

I encourage people to think about the variables effecting end results. Even specifications not discussed in literature. That's why a personal audition of the gear is so important.

I don't really agree with the assumption that SS amps are 'typically' rated for higher output power (wattage) than tube amps. Yes, transistors are physically smaller than tubes, and SS amps don't require output transformers, so SS amps can often carry higher output power ratings for a given chassis size or weight. But even this construct breaks down when considering many of the top SS amps, which because they generally require more power supply capacitance and of course heat-sinking than comparably-powerful tube amps (especially as the operational bias class creeps upward), tend to feature some pretty behemoth dimensions and masses for their rated power.

Both SS and tubed amps rated for hundreds of watts of output power can be bought. Maybe the question could be better phrased, Why are there seemingly fewer lower-powered SS designs than lower-powered tube designs? Tube fans may answer, because SS amps don't approach clipping as gracefully and therefore require higher power margins to avoid unpleasantness. Hence the nostrum that tube amps can seem to 'play' about doubly powerful compared to similarly-rated SS amps. I personally don't think that this is literally true, and that power supply robustness for rated output power ultimately has more to do with the subjective sonic result - as far as rated power levels go - than does the type of output devices employed (but also that although gross tube clipping is really no more pleasant in this context than is transistor clipping, it is usually less potentially damaging to speakers when it happens).

Mostly, it just seems that in the present market manufacturers have simply moved away from lower-powered SS amps, which many did used to make, but which now apparently fail to sell well enough (with the possible exception of integrateds) to continue justifying their production. (Some of this could have a lot to do with the HT boom.) Modestly-powered tube amps, on the other hand, apparently do still sell well (and not just single-digit SET's either). Anyway, it would usually be a mistake to focus too much on rated output power when comparing amps of different types (provided none are truly underpowered for the given speakers, room, and listener). In my own experience, I have owned a tube amp rated at less than half the output power (and twice the price, to be fair) of a SS amp it replaced and vastly preferred the former, even at higher volumes (in a smallish room).

Sean: Are you implying that some PIO or FIO caps might measure better than some audiophile-grade plastic-film types? Do you have any modding or listening experience yourself that makes you tend to lean toward one or the other for certain applications?

Oil caps are one of the original types of capacitors - usually using paper wound with foil, bathed in an oil dielectric. Often in a rectangular, oval, or round can with two terminals on one end. There are modern day equivalents, Jensen makes some nice ones (copper foil in oil, etc.), as does others (for even more money, e.g. Audio Note silver foil in oil....). Usually vintage caps are referred to as PIO. (paper in oil or sometimes poly in oil). They work great and are often used as filter caps in a tube amp power supply (probably their best application). Also good in crossovers, and sometimes as coupling caps between (tube) amp stages. Fairly easy to find the old ones, commonly they are available from 200v - 1000v ratings, sometimes higher. Usually values range from 1uf to 20uf but sometimes as high as 40 or 100uf for more modern ones. Modern applications include motor run caps (for DC electric motors).

-Ed