I have bought a VAc CLA-1 preamp

Perhaps this manual may help, it is for CPA-1/CLA-1.
If not, try to contact VAC. Kevin Hayes is always very helpful.

Cheers,
John

My original reco was just to help you identify the tubes that you have. I see that everyone else is chiming in with their personal favorite NOS tubes. I have heard them all, Siemens, Telefunkens, Amperex, Mullard, etc. To be honest, they all have their strengths and weakness'. All are much better sounding than current stock Russian/Chinese tubes.

I would say that the Mullard's are the warmest, if that's what you seek. The Telefunken's are also warm, but with a tad more air than the Mullard's. The Amperex and Siemen's offer even more extension in the high's, but are not quite as warm (sweet). Currently I am using Telefunken's in my VAC line stage (and phono stage) and I am quite happy with the sound.

Cheers,
John

PS: according to the VAC manual the four tubes are (2) 12AX7's and (2) 12AU7's.

They should be the same sonically, the difference being that the CPA1 is a full function preamp (with phono stage), whereas the CLA1 is a line stage only.

Cheers,
John