neon bulb noise? - Page 1
Forum section: electronics / projects

author: ftransform
author_rank: Frequent Contributor
timestamp: June 28, 2013, 01:25:46 am
content: So a bit of a neurotic question but is a neon bulb to be considered a noise source? The reason why I ask because I see a vague familiarity to a spark gap transmitter.I was thinking about using a neon bulb as a indicator for power in the front of a little fixed PSU I am building, it would be located on the back of the device near the mains transformer and the light would be brought to the front via an acrylic light pipe. I figured that routing mains wiring to the front of the case near the filtered DC output would definatly have an effect, but is the bulb in the back any kind of bother, say compared to a regular resistive lamp?

author: lgbeno
author_rank: Frequent Contributor
timestamp: June 28, 2013, 01:48:37 am
content: Interesting question. Does a neon bulb draw a dc current? Some of the ones that I have seen seem to flicker when they are lit.

author: c4757p
author_rank: Super Contributor
timestamp: June 28, 2013, 01:52:03 am
content: Do you have an oscilloscope and a neon bulb?

author: ftransform
author_rank: Frequent Contributor
timestamp: June 28, 2013, 02:52:14 am
content: Quote from: c4757p on June 28, 2013, 01:52:03 amWhat I don't have a is a thermal RMS meter. yet. or a isolation transformer. or a preamp for the rms meter.I suppose I can build a preamp for my multimeter but I supposed I would just ask while I have this project on hand.

author: c4757p
author_rank: Super Contributor
timestamp: June 28, 2013, 03:00:46 am
content: You're a function generator, MOSFET, inductor, capacitor and diode away from having a power supply that can light up a neon.For what it's worth, I have a couple very low noise power supplies that use neon indicators right on the front panel, with no filtering of the power or shielding for the mains wires running to the lamps. I don't know how noisy a neon lamp is, but I don't think it's going to be an issue.

author: edavid
author_rank: Super Contributor
timestamp: June 28, 2013, 03:10:11 am
content: Yes, they produce a lot of excess noise compared to a resistor. No, they don't radiate enough to worry about.

author: ftransform
author_rank: Frequent Contributor
timestamp: June 28, 2013, 03:13:18 am
content: Quote from: c4757p on June 28, 2013, 03:00:46 amand you are one post away from edavids easier post.One day I will replicate the nanovolt linear regulator noise experiment...This power supply I am building is just going to be some filtered LM317's so I can throw a bench tested piece of hard ware under my bench powered up for a long while without it getting in the way of other projects for long term drift measurement and burn in.I will measure this stuff one day.

author: ResR
author_rank: Regular Contributor
timestamp: June 28, 2013, 03:42:25 pm
content: Neon bulb creating noise... Hmm. There is two different thing between neon bulb and spark gap, the neon lamp is low pressure gas discharge bulb, where electrons collide with atoms, making it lose electrons and when it regains electrons back, it emits light that is specific to the element used, while the spark gap relies on a pure electrical arc that creates a wide spectrum of energy, including UV radiation and lot of noise. There is no need to worry about neon bulb indicator, it is not as noisy as silicone (Si) semiconductors like rectifier diodes, only little bit more than a resistor, but it is too insignificant to be a problem, mate.

author: ftransform
author_rank: Frequent Contributor
timestamp: June 28, 2013, 04:05:18 pm
content: Quote from: ResR on June 28, 2013, 03:42:25 pmI did some research and it seems that people on audio forums complain that these bulbs create noise and it leads to a squeel being picked up, which is destroyed when the bulb is removed or the current to the bulb changed. There are no explanations for these mechanisms though. I don't know the lay out of the devices they speak of though, I doubt the bulb is behind a transformer if this happens.Wikipedia says"In these applications the lamps are operated either in 'starvation' mode (to reduce lamp-current noise) or in normal glow discharge mode; some literature references their use as detectors of radiation up into the optical regime when operated in abnormal glow mode. Coupling of microwaves into the plasma may be in free space, in waveguide, by means of a parabolic concentrator (e.g., Winston cone), or via capacitive means via a loop or dipole antenna mounted directly to the lamp.Although most of these applications use ordinary off-the-shelf dual-electrode lamps, in one case it was found that special 3 (or more) electrode lamps, with the extra electrode acting as the coupling antenna, provided even better results (lower noise and higher sensitivity). This discovery received an application patent (Kopeika et al.)"I am not worried, only curious at this point.

author: G7PSK
author_rank: Super Contributor
timestamp: June 28, 2013, 05:47:02 pm
content: Neons are often driven through a resistor, any capacitance in the circuit will create a Pearson-Anson oscillator. This could be where the noise come from.

author: c4757p
author_rank: Super Contributor
timestamp: June 28, 2013, 05:51:04 pm
content: Quote from: G7PSK on June 28, 2013, 05:47:02 pmHad to Wikipedia that one, I'm not too knowledgeable about old-fashioned oscillators. What a gem:QuoteOh, Wikipedia...All the functions of the 555 indeed...

author: SeanB
author_rank: Super Contributor
timestamp: June 28, 2013, 08:33:41 pm
content: Neons are not really noisy, though the mains wiring to them can conduct mains noise into the circuits at the front panel. A 47k 0.5W resistor in each lead to the lamp though will reduce this to a low level, and it will be less than the resistor noise. Using a light pipe will work well to do the light, but you might not have a very bright indicator, good at night but not so good in bright daylight.

author: G7PSK
author_rank: Super Contributor
timestamp: June 28, 2013, 09:25:13 pm
content: I once had a massive spot welder (90KVA) that used whole banks of neon timer circuits and two water cooled ignatrons. I have also seen plugboard lathes that used neon timers as well.

author: ftransform
author_rank: Frequent Contributor
timestamp: June 29, 2013, 05:20:42 am
content: Why did we get away from neon....Will one day someone invent the contemporary neon circuit?Is there room in the hobby market for neon bulb function generators?I want one.

author: Stonent
author_rank: Super Contributor
timestamp: June 29, 2013, 05:30:09 am
content: That makes some sense now because in older electronics I've seen one or more neon bulbs inside but mounted in a way as if to say "No, I'm not a neon bulb, mind your own business" and their light shielded from view.

author: ftransform
author_rank: Frequent Contributor
timestamp: June 29, 2013, 05:32:18 am
content: I have ran into spark gaps that I thought were neon but disappointed me later.

author: SeanB
author_rank: Super Contributor
timestamp: June 29, 2013, 10:04:12 am
content: The issue ( not really) with neon lamps is that you need to have the electrodes made from either thoriated steel or you have to put a spot of Americium or another long life radioactive inside to stimulate emission from the cold cathode. Has been a big problem with EU made flourescent lamp starters, as the removal of the Thorium from the starters ( around 1kg per decade is used, it is less radioactive than the gas lamp mantles that are thrown out with no control and which dump particles into the atmosphere as they are used) made it so that they need either light to start or a much more controlled fill of penning mixture so they actually start in under a minute, which they will do from natural cosmic rays hitting them.