Tubemonger.com has good tube photos, in their tube picture library, that'll probably speak more clearly than my words. Try this, this, or this. Note some subtle variations in internal construction, shown in the second and third photos. The EIA/manufacturer code for Tung-Sol is "322," and usually appears somewhere on the tube.
Whatever you do, don't buy one that's marked "Made in Russia" and looks like this. Not that it is bad (my fave new-production), it just doesn't approach the ol' original's amazing clarity.
