Here is a link to a discussion of your question:
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1278987403&read&keyw&zzaesthetix=calypso
The made in Heerlen, Holland Amperexes are very good tubes. They were sold under a variety of labels but can be identified by a left facing right triangle etched into the glass. I would be worried that yours are getting old given the age of the preamp. I would get them tested if you can. The consensus of the discussion linked to above is that the 12AX7 contribute more to the sound quality than the 6922s. So you might want to try a pair ofgood quality current production 6922s and try some different NOS 12AX7s.
Good luck and Enjoy!
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1278987403&read&keyw&zzaesthetix=calypso
The made in Heerlen, Holland Amperexes are very good tubes. They were sold under a variety of labels but can be identified by a left facing right triangle etched into the glass. I would be worried that yours are getting old given the age of the preamp. I would get them tested if you can. The consensus of the discussion linked to above is that the 12AX7 contribute more to the sound quality than the 6922s. So you might want to try a pair ofgood quality current production 6922s and try some different NOS 12AX7s.
Good luck and Enjoy!