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"Richard Staples" wrote in
message It has always been my understanding that vacuum tubes actually generate noise when used in circuits and this noise prevents tubes from achieving the same signal to noise as a solid state or transistor circuit can achieve. *everything* generates noise, its just a matter of how little or how much. As a rule, transistors and ICs are quieter than tubes for audio, but in some cases that's not a given. I recall that during my early days in amateur radio someone even developed a procedure whereby some of the tube in the receiver circuit were converted to a solid state tube to help reduce the noise inherent in tubes so that extremely weak signals were not covered by not only normal atmospheric noise but that PLUS the noise added by the tube circuits. There have been solid state devices that plug into tube sockets and perform in a similar fashion. However, its not a given that they will perform better. They are usually chosen for their longer life. I asked a former NASA engineer about tube noise and he dismissed this by saying that it was not so much the tubes themselves but other noisy components in the circuit like capacitors and resistors and by carefully choosing the appropriate devices for the circuit that today you can now design a very quiet tube circuit. It's always been possible to design tubed circuits that approach the noise performance of solid state. It usually just costs more and you end up with something that has other difficulties such as size, heat, and other performance parameters. For example, due to impedance matching considerations, an input transformer is required to make a tubed mic preamp whose quietness approaches that of a fairly inexpensive SS equivalent. Unfortunately, the transformer is costly and causes other problems. |
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