Yes, the light tent makes a big difference. Your necklace is also benefiting from reflections from the bust it is mounted on.
Below is a basic set-up I use for the shots I posted (diamond rings etc are a lot trickier). Firstly though you used the term 'bulbs', do you mean fixed lighting not flashes? If so, then I should note that this will make the control much more difficult. Fixed lights do make it a bit easier to see what the end result will be, however colour temperature issues will raise their head, plus possible voltage variations (are you on 120v?), and unless you're using high wattage (and hot) studio lamps then contrast is likely to suffer as well. So, the basic set-up
1. A flash mounted overhead at a steep angle i.e. slightly from the back. Whilst I use a 300w/s adjustable studio strobe, camera units like the SB800 (in my case Canon 580EX II) have (just) enough grunt. This supplies the main light source into the tent. The important thing is that this is diffused otherwise the light will still be too hot. I use a 600 x 700 soft-box on the strobe, quite close to the tent. You can also use the SB800 in a soft box however you will be lowering its effective power somewhat. The result is a 600x 700 even light source onto the top/back edge. Note - this location assumes you want a slight 'overhead' look to the lighting. You just change the position of the main light source (and balance lighting) depending on your desired end result.
2. Balance lighting - I then use 2 (or more) of my 580 EX's from the upper/front corners to control the amount of shadow. With this type of work you really do need to have flashes that have variable control (which your SB800 does have).
The actual location of these varies of course depending on the object's shape etc, but the above is a good starting point.
3. It is also desirable to diffuse the balance units, some inexpensive shoot through umbrellas will work well and are quicker to set up than soft boxes. Reflective umbrellas are ok too however they reduce the effective power more. Bottom line is that you're trying to present a broad light source to the tent. As you suggested you can move them away but this is not as effective as a diffuser (and you need a bigger room). BTW push on type diffusers for the flashes are of minor use in this scenario.
4. Specular highlight control, - two things to note:
a) the more diffused lighting (described above) will create a softer transition to these and produce a less harsh look.
b) you can also temper these by using black card on sticks to shield the edge/surface - the trick is to figure out where the light is coming from - diamonds/faceted gems are a whole new world of pain
c) of course you're shooting in Raw
, and can thus use highlight recovery tools (such as found in Lightroom) to improve this further before running it in HF (note the same setting must be used on all frames).
5. Flash control, whilst I use low cost eBay wireless remotes, I could also use one of the 580EX to control the other 580's and the sensor on the studio strobe.
6. Sometimes I leave the front of the tent open to create a 'black hole', all depends on the subject, normally I leave it off while getting the position and basic exposure/lighting right, then try it with/without . Ah, the beauty of digital - instant feedback at no $ cost for film/polaroids.
BTW I could have had almost shadowless lighting on the necklaces pictured, however IMO this makes them look less real. Also most off the time I use white backgrounds as my clients want masked items to enable them to be used with various backgrounds.
Here is a link to a post I made in the Gallery showing two more items
. The diamond ring took about an hour to set-up, shoot and HF, then another two hours of post processing to get this look (the unfocussed band at the bottom is deliberate, done by using gradient blurring in PS)
Lastly, may I recommend visiting the strobist site at http://strobist.blogspot.com/
, this is an excellent resource.