bmw@aesat.UUCP (Bruce Walker) (09/19/85)
[Articles are packed by weight; contents may settle during shipping] In article <5700094@uiucdcsb> jabusch@uiucdcsb.Uiuc.ARPA writes: > > Yes, all TV's are this way... the high voltage required to drive > the electron guns has to be DC. The standard way to create this voltage > is to generate a low-frequency signal [...stuff removed...] [...] > The problem with these circuits usually starts when the original > oscillator goes off-frequency a little. Since this oscillator runs around > 20KHz, any variation can throw it into audible range. [...] Not quite. The flyback transformer is part of a sawtooth waveform generator that is phase-locked to the horizontal sweep frequency which, in the North American TV system, is supposed to be 15.75 KHz. This is *already* audible to most young people and a lot of older folk as well. I agree with your other comments about vibrating parts, ageing components can cause the most horrendous squeals from TV's. > Dimmers are not always > potentiometers, but are occasionally made of oddball parts. I have seen > the internals of a few, and would hesitate to guess what exactly is being > done internally. Dimmers are *never* pots (at least not since the thyristor (1960's?)). The average dimmer uses a triac (sort of a bi-directional silicon switch) to control how many degrees of each half-cycle of the 60Hz line will be applied to the light bulb. If the bulb "sees" 180 degrees, it's full on; if it sees 90 degrees, it's about half bright, etc. The pot controls the phase angle (number of degrees) until "firing" the triac. Buzzing sounds coming from a dimmer are probably caused by some component breaking down (ageing) a bit inside. My guess is that one of the larger capacitors' plates are vibrating. Most cheap light bulbs will whine or buzz when dimmed sufficiently, this is just an indication of the poor design of the filament. If one springs for a $6 Splendor spot light (for track lighting), you will never get any annoying sounds from your lights. Bruce Walker {allegra,ihnp4,linus,decvax}!utzoo!aesat!bmw Join the march to save individuality!