What tubes do I need?

I have no experience with tubes other than owning an Atma-Sphere  amp and preamp.
My suggestion is to PM Ralph Karsten (atmasphere). He would be likely to be able to help you discern what tubes are in your preamp.
Plus he's a nice guy who always tries to help out here on Audiogon.

And, I wish I could visit Stockholm.
Bob

you should consult your owners manual or literature for that specific preamp you own - don't rely on what the prior owner may have told you

one number or letter off on the tube type it is an entirely different tube! close doesn’t count!!!

Put the originals back in and verify the amp is still operational.
Hopefully it is.
Then compare the tubes internal structure, size etc. While tubes of the same type exhibit many variations, it is possible to see enough similarities. See if there are any markings that might help with identification.

Just take some closeup photos of the original tubes and upload a link to the pics here someone maybe able to tell. Make sure you get detail of the  insides of  the tubes.

I'm not familiar with this company.  I assume they are no longer in business so you can't check with them?

Audio Matiere used ecc88/6dj8 for line stage/level and ecc83/12ax7 for phono stage/level, plus other rectifier tubes and sometimes El84’s (?) in their preamplifiers.

The US importer of Audio Matiere seems to still be in business (selling other goods now) and you might try sending them an Email.

http://marigoaudio.com

As suggested put the old tubes back in to see if it still operates.

If the circuit was designed for ecc88/6dj8 and you ran an ecc83/12ax7 in it it should still hopefully be OK as you barely powered/heated the 12ax7, but I would suggest not doing it again.

PS:  Do not put an ecc88/6dj8 into an ecc83/12ax7 position/socket as you would be supplying 12 volts to a 6 volt tube (if the ecc83/12ax7 is wired for 12 volts). 

DeKay