Mesa/Boogie Bass 400+

[scottblessed]

found this neat wee tip on www.talkbass.com and have been meaning to do it for a while and finally got around to it today.

Basically, what you do, is swap your drive tube in the pre amp (tube closest to the mid control) from a 12ax7 to a 12au7.

Wow, the results are unbelievable, instantly, the EQ becomes more apparent and much more responsive.

Seriously, those who know about this, try it, and those who don't, get on it and make your amp instantly better.

Before, I would find myself using the switch pulls to get good, round bottom end with defined highs, usually, my amp would be set at mid-7 bass-4/5 (sp) treble-4/5 (sp) with the input gain cranked to between 4 and 7.

Today after changing the tube, mids were at 8, bass was at 3 and treble was at 0 and it sounded better than it ever has before.

thanks for reading.

[gypsymoth]

a 12at7 would likely do the same thing with less drop in volume.
might not matter so much in a 400.

[Kiwi]

I have to admit I'm not exactly clear on why there would be a difference, would someone mind explaining?

[gypsymoth]

at7's have less gain than an ax7, au7's have far less.

so even when pushed there may be less distortion than an ax7 at lower settings. slightly different voltages as well.
I'd expect an at7 in V1 and as driver would yeild a "better" result than an au7, but as with all things of this nature, it is a matter of taste.

generally I don't think it is worthwhile/better, but it would depend on the amp & ears involved.