What is the "best" of the 5881 Tubes.

I like the old stock Tung-Sol 5881's.

That being said, I've not tested that tube type in several years.

The only 5881's I heard were Sovtek's so I can't judge. However, somewhere I read that your amp would take 6l6gc's. If that is so I would recommend the SED 6l6gc. Its a great tube, especially thru the mid range.

Tubby:

Check out this thread:

http://forum.audiogon.com/cgi-bin/fr.pl?htech&1143225993&read&keyw&zzonix

Before you touch the 5881 tubes (which are basically the military version of the 6L6) in your new Onix SP3, do yourself a favor and install a pair of the Groove Tubes 12AX7-M "Mullard Reissues." You'll find the bass to better defined and the mids livelier without giving anything up in terms of detail and speed. The Chinese stock 5881s are decent, and you can get more mileage out of changing the 12AX7 preamp tubes.

If you have the itch to change the four power tubes, get a matched quad of the SED "Flying C" 6L6GC tubes, and adjust the bias of the tubes accordingly.