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Thanks for the improved explanation. Valves are naturally current limiting because of the emission limits on their cathodes they are also connected to loads via transformers which are also power limiting devices so short circuiting them does not usually blow up the amplifier. Valves are also physically larger hotter and the power densities are much lower and no special heat management techniques are needed. Transistors however are current operated devices that are connected almost directly to the low impedance load that loudspeakers usually present and unless there is a protective circuit in the design to limit the drive to the output stage when overload is detected very large currents can flow. Transistors are also much smaller and operate at higher power densities and damaged if junction temperatures get above 150deg C so they need heat sinks and sometimes fans to keep them cool. Brief overloads can easily damage them.
Vacuum tube amplifiers tend to produce predominantly even ordered harmonic distortion, rather than the predominantly odd ordered harmonic distortion produced by solid-state amplifiers and in listening tests most people seem to find even ordered harmonic distortion preferable, and even beneficial to the music, compared with odd ordered harmonic distortion, which most people find positively objectionable.This is especially noticeable with electric guitar amplifiers, where some degree of distortion is more or less essential; an electric guitar played through a very 'clean' amplifier tends to sound rather lifeless and dull when compared with the same guitar played through a vacuum tube amplifier, even when the vacuum tube amplifier is set to produce little audible distortion.When high levels of distortion are actually wanted, there's really no comparison between the qualities of the two types of distortion produced: the 'natural' odd-ordered distortion produced by solid-state amplifiers sounds wasp-like and buzzy, whereas the even-ordered distortion naturally produced by vacuum tube amplifiers tends to sound thicker and more smooth or 'creamy'.
"Early semiconductor electronics in this state would burn out in seconds of losing the load". This statement really puzzles me, they never do nor never have cared about losing the the load (ie running into an open circuit ) this was one one of the things I really liked about transistor amplifiers when they first came in.
So to a trained ear (e.g. a musician) would rather desire the vintage vacuum tube amplifiers?
Quote from: tommya300 on 13/07/2010 01:11:22So to a trained ear (e.g. a musician) would rather desire the vintage vacuum tube amplifiers?Well no, not quite. They'd probably prefer an amplifier that produced the least distortion.Also, you seem to have fallen into the trap of assuming that all vacuum tube amplifiers are old i.e. 'vintage', and ended up drawing the erroneous conclusion that all vacuum tube amplifiers are therefore more primitive and inferior in comparison to modern solid-state amplifiers.There are quite a few very modern vacuum tube amplifiers around but because the thermionic valves are much more expensive to produce, not only because of their mechanical complexity but also because of the reduction in the scale of manufacturing, modern vacuum tube amplifiers tend to be considerably more expensive than an equivalent solid-state amplifier.
Valves are big. They can absorb a fair amount of energy without heating up much. Transistors are small. They can not.Also, a valve can survive being baked to a few hundred degrees; it will work fine once it cools down again. Transistors fail, irrevocably, below 200C.If there is some glitch that means that the power that is meant to be fed to the speaker gets dissipated in the valve or the transistor, the big heavy slow thing is more likely to survive because iyt won't get as hot, and if it did, it wouldn't matter so much.You really don't need anti-static packaging for valves.
Open circuit the power has to go somewhere, if there is no load would it also heat up and allow fry these stages. Not to mention sometimes feedback. Am I close or an I a bit disillusioned in this area? From time to time this happens?
Quote from: tommya300 on 13/07/2010 01:42:14Open circuit the power has to go somewhere, if there is no load would it also heat up and allow fry these stages. Not to mention sometimes feedback. Am I close or an I a bit disillusioned in this area? From time to time this happens?No load, no current, no power, just voltage rail to rail.
Geezer, you have never used bipolar RF power transistors, they are very static sensitive, not to mention load sensitive, heat sensitive and also have that lovely pink ceramic casing that carries the tag Beryllium Oxide - Caution Toxic. Only good thing was that when installed they really work well.
Ah yes! The 3055 would not be the ideal choice for an output stage.
Geezer, I worked on equipment that was poorly designed, and had a switching transistor that was poorly heatsinked, and badly driven. Peak current was 40A and average was 10A, well beyond your common 2N3055. I used to select the transistors based on BE saturation voltage, as a few mV here made a difference ( along with selecting a 2N2219A driver that had a high gain and would saturate with the limited drive) between surviving a while or going short circuit in worst case or merely unsoldering itself at best. Eventually I got a good batch of BUX40 that would survive, the batch was at the top end of spec for Hfe and most did survive.A 2N3055, depending on who made it, often has a gain roll off at under 10kHz, not what you would like in an amplifier. I did use some as active loads, by soldering leads onto then and dropping them into a ceramic cup ( old tea cup) filled with cold water. Driven with a 555 timer and used to test power supplies for load stability, they generally worked well until all the water had boiled off, then glowed white hot and burnt out.