dsavitsk

None of these (other than the EL34's) appear particularly valuable. These are about equivalent to the 6CD6GA. Decent power tube, but has a lowish screen grid limit. Could be used for a few watts in a power amp -- I wouldn't both for headphone duty. http://frank.pocnet.net/sheets/127/7/7867.pdf Here's a schematic using one, which you'll notice uses a lot of your tubes which may not be coincidence: http://www.triodeel.com/du1a475.gif Another low power output pentode (much lower power than the one above). Might be useful for a transformer coupled SE amp of some sort -- good for a couple of watts pentode, or less than a watt triode. http://frank.pocnet.net/sheets/127/2/25C5.pdf Close to an EL84, lower plate voltage iirc -- one of them is not going to do much for you.