What is the purpose of the small neon bulb by the flyback on older TVs? = (I haven't noticed it in any modern tvs.) Someone asked me that the other day and I couldn't answer! Seems like I = used to know (I'm an old-timer) but can't remember. Thanks.
Are you sure it is really a neon bulb? I'm thinking it is possibly a high voltage spark gap which serves as overvoltage protection... Just my thoughts. Without seeing it it would be hard to say for sure.
Yes, I'm sure, was a small glass neon bulb soldered to chassis. I looked through a good many old Sams folders, back into the '70s & '80s = but never found a neon bulb in one. Problem is, just because it was near = the fly doesn't have to mean it was in the fly circuit. So it must have = been in some other circuit. I think it was for spike protection, for = whatever circuit it was in.=20 I'm ready to just forget it, not important.=20 Thanks to all for replies!
A real neon bulb? I wish I owned a million of them, I love neon lights/neon signs.I own an old broken neon NO VACANCY sign I bought at the Goodwill store years ago.It was broken when I bought it.I like it anyway.I think it dates back to the 1940s or 1950s.Nothing beats neon lights and neon signs. cuhulin
I think it was used as a high-voltage clipper... sort of a high-voltage zener diode. During normal operation it's never supposed to light up. I often saw those on neck boards of old monochrome video monitors. Only once did I ever see one light up and that was due to picture tube failure (the precise details of which I can't remember now). The firing voltage of neon bulbs is pretty high... at least 50 volts, some go as high as 90 volts.
BTW: If the bulb is placed across DC, only one of the interior electrodes will light up. If the bulb is placed across AC, then both internal electrodes will light up.
If it was a true neon bulb, then it wouldn't actually need to be connected into any circuitry in order to light up as an indicator of flyback activity. Most gas filled tubes will light in mid air if they are in close enough proximity to a flyback tranny. Back when I was an apprentice, like 35 years ago, the guy that I worked under in a TV workshop, used to keep a short thin flourescent tube on his bench. He used this to test for horizontal output stage activity, simply by waving it around the FB tranny. As I recall, he used to reckon that he could tell a lot about how that stage was working, when he had a lack of picture fault, just by the 'way' in which his little tube lit up.
Most of the similar 'bulbs' that I've seen on CRT base connector boards, have been gas-filled spark gaps. I seem to recall that they used to put argon in them, and when they went off as a result of an inter-electrode short in the tube, they lit up white, rather than the orange glow of a neon.
I know all about this. I run a farm. Around the livestock I have electric fences that normally put out about 5 or 6KV. (less when wet or being touched by weeds). Although I have a tester that connects to the wire and tells the approx voltage based on the number of neon bulbs that light, it requires connecting it to the fence and a ground. Often I just want to know if the fence is working. I have a short florescent bulb that I took out of an old kitchen range. All i need to do is hold it a few inches from the fence and it will light if the fence is working. I even made a holder to keep it in place so I can just look out the house window and see if it's glowing. That worked until a pony decided it was something to play with.
Either way, it works well as a quick test.
To the OP of this message, I do recall seeing the neon bulbs in the older tvs
Which reminds me. I have an old neon bulb nightlight. This thing is confused and retarded. If the room is dark, it does not light. But when I flip on the ceiling lights in the room, or point a flashlight at it, the neon lights up.... I think it's just plain old, but I leave it there just because it's a conversation piece.
Believe it or not, this is more or less normal for an old neon bulb.
Ambient light knocks electrons off the neon atoms in the bulb, _lowering_ the threshold voltage. This bulb has aged to the point where the line voltage isn't high enough to light it _until_ room light or a flashlight "kicks butt" on them-there outer-orbital 'lectrons.
My old NO VACANCY neon sign is an old metal box, the old brown paint on the box is very faded.The neon glass tubes, some parts of the glass tubes are completly broken away, missing.The box still has the old high voltage power thingy in it.I don't think there is anybody in my local city area who builds/repairs old neon signs.I only hang onto it because it is very old and I like to collect all kinds of very old things.The Postman Always Rings Twice old movie.That poor cat got zapped on that neon sign. cuhulin
William Sommerwerck wrote WITHOUT ATTRIBUTION TO THE PREVIOUS POSTER:
Yup. In the '60s, electronic organs used neons in their percussion circuits (e.g. a Xylophone tab). Incandescents were positioned inside the unit near the neons so that NE-2s were "biased". When someone said his precussion stopped working, you made sure your stock of mini incandescents was up to snuff.
Or just send the glass out to have it fixed properly. I dunno how it's possible to live to far from a neon shop, there's lots of mom & pop joints still spread around the country. The craft nearly died out for a while, but in the last couple decades there's been somewhat of a revival. Once have the sign box with the transformer, it's not terribly expensive to have new units made for a simple sign like that.
There's LED "neon" out these days, but nothing comes close to the real thing, it just doesn't look right.
Yup ! 'Neon' tubework has a look all of its own. When I first went to Vegas probably 20 odd years ago, it was all neon. Now, with a few exceptions like the main signage at Flamingo, and one or two machine banks on the casino floor, the Strip is now predominantly lit by LEDs and LED giant screen TVs. There's still some original-style neon tubework downtown at the Golden Nugget and so on, but not a lot any more. The neon had a much more 'organic' feel about it, I think. Kinda like the difference between film and video. Still very pretty there, and unlike anywhere else on earth, but not quite as 'warm' feeling as in the old days ...