Hi i was posting here that i was looking at an avalon M5, well a friend of mine told me to look at the avalon 737sp to use with SX 3 and an RME 800, however i have a friend who is a Ph. D in Physic's from MIT and CMU and i was asking him about these "military tubes" that avalon brags about. here is his reply, if this is true does anyone here know of a really good solid state pre amp/comp/eq?? see i should never talk to these people cause it KILLS ME''thanks for any help ___________________________________________ Tubes do go bad, and they are very expensive to replace at this point. The real problem with vacuum tube stuff is that tubes by their nature are high impedance devices, whereas the loudspeakers are all (to the best of my knowledge), are low impedance devices. You probably know this, as speakers are generally 8 ohms. I think I have seen some sixteen ohm speakers in my day, but they are few and far between. Tubes are essentially voltage driven devices, and their internal impedances generally are in the thousands of ohms. Tubes don’t like high currents. Transistors, on the other hand, hate voltage and love current; they are low impedance devices. In order to transfer power from one device to another, say an amplifier to a loudspeaker, in order to have good efficiency you have to “match” the impedances. For optimum efficiency the output of the amplifier should be 8 ohms to match an 8 ohm speaker. If it is higher than that, not only will you not transfer power efficiently, you will also reach distortion levels sooner, because the possible voltage excursion of the tubes (limited by the power supply if nothing else) isn’t great enough. To get around that problem, a high quality audio amplifier will have a huge matching transformer. This works, and does a good job, but the iron in the transformer must be of high quality and there has to be a lot of it to achieve reasonable power output. So the high quality amplifers of the 60s generally had a huge output transformer that cost a lot, weighed a lot, and took up a lot of real estate on the hardware. You couldn’t even mount one on a circuit board. A good transformer for a 50 watt amplifier, not that big by today’s standards, would weigh fifteen or twenty pounds. Admittedly, there are ways to avoid the output transformer, but why bother when transistors do the job with great ease. I have heard audiophiles say that they can tell a difference between solid state and vacuum tube equipment, and I don’t doubt that that is true in some extreme cases. However, what they may be hearing is distortion introduced by the vacuum tube stuff, and they have grown so accustomed to it that they feel lonely when it is not there. The thing to look at is the harmonic distortion at rated power output. The one with lower harmonic distortion wins. Probably more than you wanted to hear. Save your money.