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Tube Question


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ok, first off, i have a crate blue voodoo head (BVH-120) it runs 4 5881's and 4 12ax7's, now, my question... will it only take 12ax7s? or can it take the 12AU7, 12AT7, etc.? would it need to be rebiased?

for another question that has nothing to do with my amp... i was checkin out the new guitar one mag, and they had an ad for the new B-52 all tube head. i was wondering... what is the point of having a tube effects loop and a tube phase inverter, and what is a phase inverter.

thank you,


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biasing is for the power tubes,not the preamp tubes(12ax7 are preamp)if i remember right.

go to


they have a q& a section which is very informative

that being said...for metal i think you are best to stay with a high gain 12ax7

but there are many to choose from...some provide a more harmonically rich tone,some provide gain with or without harshness....you just have to read the description and make a choice.it may take years to find exactly what you want...and then they may start making them in a different country. :D

but if you are happy with the blue voodoo sound(which is pretty dang good..at least the one i played at guitar center)then just leave it alone

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you can and sometimes do have to rebias the powersupply to serve some preamp tubes you need to look at what sound you want vs what you already have. a 12at7 is a little over half the gain of a12ax7 a 12au7 draws way more current than a x7 all though they will work as a direct replacement there are bigger issues to address. along those matters. for high gain stick with the 12ax7's to clean it up a little go with a 12at7 in the first slot.

the phase inverter is a tube that flips the positive wave form that your preamp produces [note i am saying positive due to simplifiy things here] and it inverts it to create a negative wave form so that you sine wave square wave sawtooth whatever wave form travels through the zero marker and into the lower region and back again. as your power tubes each run half of the signal so that in an ideal situation you get the amp is maximizing power to the side of the amp that is actualling reproducing the freq at its given phase at that moment. kind of like a V-8 engine.. each piston doesn't fire at exactly the same time or it would just split the shaft. hope that wasn't to vague. :D

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