i'm looking at getting this amp at the end of october and i was wondering how long the 12ax7 valve would last before it needs replacing. i am aware that it works as both a power amp valve and a pre amp valve, and i heard that power amp valves have a tendecy to blow quickly. i would be using the amp from anyware from 30 mins to an hour or maybe longer a day. so how long do you think i would have before the valve blows. i want to know so that when i get the amp is there any need to pick up a spare 12ax7 valve incase it blows on me, as i live a few hours drive from anywhere that would stock valves.
The power amp is solid state I believe(Could easily be wrong). I think the tube in the preamp is there to give the amp some more tube-like dynamics and feel.

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The valve will never go in one of these amps. It isn't running at high voltages like in all tube amps. It should never need to be replaced.
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The tube is used as both power and preamp, while it is a preamp tube. It's more or less just a gimmick. It won't blow that easily.
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Sampy's right. For the record- power amp tubes do not "blow up", they simply wear out after some time, like lightbulbs etc. The tempo of this depends on how you use your amp - if you play LOUD and really, really often, really long, they will wear up after a year or two, I think. If you use it on bedroom volume levels and for an hour a day, it might take even longer.

Oh, and I've tested Vox VT30 and IMO it sucked terribly, sounded really fizzy and far too trebly, too much 'sand' in the tone, AD30 I've tested was much much better sounding. Maybe the one I've tested was faulty, but I've checked some YouTUbe videos and they all sound pretty similar to me.