Hookup wire for tube amplifier?

Ralph makes some good points. The OCC is a casting process, not a ranking of purity. The other point many will make is, "does it matter" whether it is OCC? The Jupiter wire is CDA-101, which is thought to be the highest purity - it is 99.99 percent pure copper. Measurements show the conductivity of ETP copper is the same as OFC or OFHC copper. I certainly don't have the answers, but I can say the Jupiter wire (in the configuration I use for IC's) sounds very good in my system against some other well regarded wires. I suspect dielectric material and surface condition of the wire, along with other factors, could all play a part in the sonic performance of wire/cables. I particularly like the following from one of the attached links;

Copper of extremely high purity, or with large crystal size are also available, sometimes at a high price. Whether they have any value in such applications as audio speaker cables is at best unproven, there being no measurable improvement, and some negative results from subjective blind tests. (Not to mention claims of positive results from non-blind tests where dramatic differences were invariably described for what were believed to be known different cables, when in fact the cable was never changed.) Blind testing is sometimes dismissed as too intimidating by believers in 'cable effect', and yet the language used to describe cables suggests gross effects easily audible, e.g. someone claimed that his wife rushed through from the next room to find out what had happened when a cable was changed, the effect was so dramatic. This does not suggest some minute effect only audible under ideal conditions.

Links:
http://www.angelfire.com/ab3/mjramp/ofc.html
http://www.angelfire.com/ab3/mjramp/wire.html
http://en.wikipedia.org/wiki/Oxygen-free_copper
http://www.sequoia-brass-copper.com/alloy_101_ofe_copper.htm
http://www.6moons.com/industryfeatures/caelin/caelin_2.html
http://www.southerncopper.com/metals.asp?

I don't think any generalizations about wire hold true. There are good examples of all kinds of wire. I have never heard Audionote silver wires to sound overly bright in any of a number of tube systems I heard them in, my own included.

The only way to know how any cable will sound in a particular setup is to actually try the cable. Most dealers allow for auditions, and there are on-line companies that have a "library" of cables that they offer for home trial.

If anyone has compared OCC copper vs silver wire, please chime in.

There are so many factors that go into wire design, not just conductor material, such as insulator dielectric properties, basic configuration of the conductors, etc., that I would never focus on design aspects, much less one particular design aspect (conductor material).

Cable companies try to distinguish their products and justify prices by touting things like silver conductors, or continuous casting, cryogenic treatment, teflon insulators, static electric charge to polarize the insulator, etc., but, the real value the better makers provide is intellectual--a combination of all factors/material into a good design and critical listening in voicing the product. Yes, it probably does make a difference whether a particular cable is made with silver wire vs. OCC copper, but, that one factor is so small a contributor to the sound as to render choice based on that alone to be meaningless.

I can appreciate that it is pretty hard for some people to actually audition components in their own system so some purchases have to be made as "informed" guesses. For that, you should generally ask around about specific cables (not designs) and find out what people have paired with their tube gear.

I have a local dealer that only sells tube electronics (aside from digital source gear). He likes the sound of NBS cables (but hates dealing with their crazy ownership), Audionote (uk) and Snake River. He said the best cables he has tried in his store is the liquid conductor T.E.O. cables, but he doesn't sell them because of the extreme price of the better stuff.

Of course 7N copper exists. It is even a subject of international conferences like this one:

http://jp4.journaldephysique.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/jp4/abs/1995/07/jp4199505C747/jp4199505C747.html

In addition to limits of purity Continuous Casting process produces extremely long crystals (many feet long) by very slow cooling of the copper in hot forms (to prevent crystallization). In comparison common oxygen free copper has thousands of crystals per foot. Impurities resides between crystals. Copper Oxide is a semiconductor.