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the tubes are kind of oddities, 6p15-ev and some chinese variant of a 6922, 6n1p-ev. these aren't the exact tubes that came with the amp; the amp is actually in my weekend home in another state and i am not able to check directly and see exactly what they are, and since they aren't mainstream tubes i cannot recall exactly. But these were the ones that i purchased as direct replacements via ebay from ukraine, and was able to check my ebay purchases to find out their type. i did some research and purchased some russian mil replacement tubes that were both highly recommended, but also the only ones really available. they are basically com-block versions of el84's and 6922's, if i remember correctly the small tube is like a 6922 with a higher heater voltage. the lil amp actually sounds pretty good, and this is coming from someone who is used to listening to a $25k tubed setup: modwright tubed oppo 95> audible illusions M3a> VTL ST-150> Martin Logans. hell any single tube in my entire chain cost more than this whole unit. it's a cool little unit, i am using it to drive some modified horn hybrid speakers, to decent effect. my russian tubes have come in but i havn't been back "home" to install them and give them a try. so all thoughts or reflections are based on the shitty factory chinese tubes that came with the unit. Tube upgrades, maybe some silver teflon wire and cap upgrades, wont be lost on this little unit. hope all this helps...