> Now you're making a connection back to the original article. That > high-pitched "whine" was from high frequency magnetic fields causing the > internal ferrous parts of the tube to vibrate. This would sometimes be > at harmonic frequencies that would cause the external tube or even the > mounting surface to vibrate, making the sound audible.
No, that is not correct. The whine or hum sometimes heard in electronics can generally be traced to cheap transformers (the laminations vibrate if they are not tight) or the hetrodyne action of two RF signals fairly close to each other. The tubes do not make noise. If the elements of the tube did vibrate so much that they could be heard with your ear, their movements would cause any signal they are trying to deal with get completely swamped out. If you have an old amp with tubes, try this - just very lightly tap the side of the tube with a pencil, and hear what sounds like a Chinese gong being struck. Movement and vibration of the elements was a very serious design issue. Officially the effect is called "microphonics", and great lengths were taken to make sure it was minimized. > Nearly all of > what we encountered tubes in as consumers were analog devices. Now put > those tubes in a computer, a digital device and start pushing square > waves through them instead of nicely curved analog wave forms. Magnetic > fields that are basically going from full on to full off repeatedly. > Small ferrous parts getting jerked back and forth all over the place. I > bet that "hummer" buzzed like a hive of angry bees. The fields in tubes were basically electromagnetic. Magnetic fields were generally kept to a very minimum. On a grid, for example, the current is tiny - almost not there at all. With no current, there is no magnetic field. -- Will ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
