[braillediver]

I believe it's bad form and against the rules to offer items for sale in other than the For Sale Forums.


Mitch

 

[drarthurwells]

I am still wondering about subbing the 12AX7 with the 12AU7 where the reduced gain is no problem.

The difference in electrical characteristics would suggest some possible bad sonic implications in doing this.

Modern amps are described as "auto biasing" but are they? Do they have a bias monitor that adjusts for tube bias changes? And would this make subbing with the 12AU7 quite feasible?

Here is one comment from someone (not on this site):

"I use 12au7s everywhere a 12ax7 is indicated unless I need overdrive
at every volume. That's why in Voxs and Hiwatts they will use 4-8
12au7 types as cascading gain blocks where 1 12ax7 would work. but
clean with a pedal or as I like a clean channel pushed all the way up
with a master volume control when needed is perfect."


Can anyone comment, pro or con, in this subbing?

 

[Balisarda]

My ZOTL was spec'd for 12AT7 tubes (gain factor 60), but Allan at Berning told me I could use any 12A_7 tube without fear of damage.

I tried a couple 12AX7 tubes (gain factor 100), but they sounded too hot, to the point of distortion.

I tried a couple 5751 tubes (gain factor 70), and they sounded fine, adding treble energy and preserving excellent dynamics.

I tried a couple 12AU7 tubes (gain factor 19), and they sounded beautiful in the mids (especially the Siemens), but bass and dynamics suffered badly, and the music sounded boring.

So you're unlikely to damage your amp (thought I'd aks the manufacturer first), but you may find the lower gain factor has effects other than just making the sound louder or quieter.

 

[babyoh]

http://www.hktubeaudio.homestead.com/files/12AX7.html

http://www.hktubeaudio.homestead.com/files/r12AX7.html

http://www.hktubeaudio.homestead.com/M8137.html

 

[drarthurwells]

Quote:

Originally Posted by Balisarda /img/forum/go_quote.gif My ZOTL was spec'd for 12AT7 tubes (gain factor 60), but Allan at Berning told me I could use any 12A_7 tube without fear of damage. I tried a couple 12AX7 tubes (gain factor 100), but they sounded too hot, to the point of distortion. I tried a couple 5751 tubes (gain factor 70), and they sounded fine, adding treble energy and preserving excellent dynamics. I tried a couple 12AU7 tubes (gain factor 19), and they sounded beautiful in the mids (especially the Siemens), but bass and dynamics suffered badly, and the music sounded boring. So you're unlikely to damage your amp (thought I'd aks the manufacturer first), but you may find the lower gain factor has effects other than just making the sound louder or quieter.

After jamato8 cautioned about differences in the 12AUu7 and 12AX7 I have listened more intensively and decided using the 12AU7 instead of the 12AX7 usually does not work out, though it can in certain combos. This is consistent with your experience.