... How to select tubes for line level preamp ...

Was you preamp modified?

The original Wolze used a 12au7 "type" along with EF86.

DeKay

The 12ax7 has approx. 5 times the gain of a 12au7 "type" tube. 

Never seen/heard you preamp but, from what I recall about it an unusual 12au7 type was used.

I may have run  across the Wolze when researching tubes for my "early" Bottlehead Foreplay 12au7 based preamp years ago, but I do not recall the specifics (certain that it was not a 12ax7 though).

I'll try searching the old Bottlehead forums tomorrow to see if I can come up with the 12au7 equivalent that I researched (like 15 years ago;-)

This said, if it has been changed/modded this will be a mute point.

I've rolled the 86 tubes in something (thinking a vintage Pilot 690 preamp/tuner), but again I do not recall specifics as this was a long time ago.

Anyway, if it does end up using a 12au7 I'm familiar with gobs of old production types and can chime in @ that point.

DeKay  

Couldn't come up with much other than a few references to 12au7 and 6211 tubes in the Wolze (along with EF86).

These came from title headings on Google, but the articles/pages were no longer available.

6211 must have been the tube I researched for the BH preamp.

Some hits to VTV magazine that I did not look at (reading VTV gives me a headache).

I understand that these were kits so anything is possible considering Wolze and the wild and crazy guys/people who most likely built them.

What 12ax7's are you currently using?

DeKay

Vintage RCA (Black & Gray plates) do have extended HF's for a 12ax7, IMO (more than the Telefunken and Mullard's I've used).

Old production Holland 12ax7's do also, but they are really expensive now.

Old production Sylvania 12ax7's have gobs of HF, but they are lacking the mid's and LF's that you like.

You might try a new tested pair of the Russian EF86's (old production winged C/SED are still available for $40/pr) in the event that yours have lost some HF extension.

Old production EF86's are also currently super expensive.

Remembered I used the EF86's in a couple of guitar amps that I was retubing for a neighbor for which I pulled a Telefunken EF86 from an old Pilot pre/tuner (don't really know how they sound in HiFi gear).

You might check prices on RCA 12ax7's (I'd look for new testing old organ stock to save money as the Baldwin (Conn?) labeled tubes were supposedly thoroughly screened for their intended purpose).

Not familiar with new production 12ax7's.

Oh, and here is a blurb I placed on favorites and forgot to include in my previous post.

https://www.audioshark.org//pre-amps-9/wolze-triode-line-level-preamp-4421.html

DeKay