NE-51 Neon Bulbs

Oh, you definitely need a series resistor. About 100K is typical.

Jon

Of 3 hits from searching NE51 - voltage rating was stated variously from

105 - 120.

Confusingly, one page displayed a picture of a filament bulb.

If a "bunch" of them is sufficient to sacrifice one, I'd peel the base cap and see if there's a resistor in there.

Anything with a plastic lens cap probably has a resistor in the base.

Ionisation voltage is usually 70 - 90V, across the mains with a 100k resistor in series would reveal the volt drop of the bulb - anything much above 90V suggests an internal resistor.

That lamp is set to operate at 120V AC, so no, you don't need a resistor. I do think they may be putting one in the base.

A NE-2 however, does need a resistor.

While some neon bulbs with a base may not need an external resistor, this one needs an external resistor.

All the data sheets I looked at states they need an external resistor , usually a 220 K .

anywhere from 100,000 - 200,000 ohms, 1/2 watt or larger. Smaller resistor, brighter light, shorter bulb life.

Thanks for the replies, everyone. I forgot to mention that my lot (about

30) is of vintage GE NE-51's, not the modern "NE-2 w/ plastic lens" variety.

Hello,

While I recall that they need the dropping resistor, since you have a bunch of them, I might try destructive testing, and break one apart to see if there is an internal resistor or not.

Regards, Tim

Madness-

NE-51 does NOT have a resistor inside!

One thing you can do with them, is build a relaxation oscillator. From a 90 to 100 volt DC source, connect a series resistor, with a capacitor across the bulb. Perhaps 470K Ohms and 1 uF. Try different values to change the flashing rate. For smaller values, it can be used as an audio oscillator.

Another variation is to have several bulbs, each with its series resistor. But the capacitors are connected from bulb to bulb in a ring. The result is a somewhat random flashing. I once built one with 5 generic neon lamps using two small 45 Volt batteries in series. Some people would become engrossed, trying to figure out the flashing sequence!

Fred

I remember repairing a church organ that used such oscillators, one for each key... That was some 40 years ago :-) Sawtooth oscillators do produce a nice sound.

Cheers!

Memory says they always needed a resistor, it's not about too much voltage, but about needed a limited current. The only time they don't need a resistor is if there is a resistor built in.

Michael

If you take this approach, it does not have to be destructive. If you own a soldering iron, you can melt the two solder blobs on the bayonet, loosen the cement, and remove the bulb intact. After inspection, you can reglue a nd resolder, and the lamp will be as good as new.

The 1966 GE Glow Lamp Manual says a B1A (NE-51) draws 0.3 mA with a 220k ohm resistor at 120 volts.

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

My recollection of playing with neons in my youth* is that they run stably at about 50V. Leaving 70V across the 220k resistor. That's pretty close to 0.3 mA. QED!

• As an apprentice project, I built a clock that used four 5x7 blocks of neons for a digital display.

Mike.

See

Mike.

Note that many neon bulbs had some sort of radioactive doping to get them to fire at a lower votage.

I don't have any hard data, but I believe it was thorium up until the late

1940's when the US government decided that radioactive material needed supervision.

It was found to be simpler to just add a small amount of radioactive krypton gas to the neon. However the half life of the krypton gas is about 10 years. So neon bulbs made in 1970 would have about 1/20th of the krypton still radioactive, which is probably no longer able to make a difference.

Speaking of radioactivity, if you are looking for an unusual project to make from them, they can be used to make geiger counters.

I don't think they are very sensitive, but if you live in the US, the red Fesita Ware department of any thrift shop would make it "go nuts". :-)

Geoff.

--
Geoffrey S. Mendelson,  N3OWJ/4X1GM/KBUH7245/KBUW5379

Most valves have some radioactive material in the cathode coating to increase emission, gas mantles also have some as it makes the illumination more intense.

IWHT: the radioactive content of a neon bulb is insignificant compared to either of those examples.

Mpfffff....

This lamp was used by Zenith and more than a few other manufacturers in the 1950s/1960s as an indicator lamp (on/off) at about the time that radio man ufacturers started to become concerned about user-servicing and hot-chassis radios - something that never really bothered them in the past. The worked on the theory that a neon lamp was far less likely to burn out than the ol d standby #44 or #47, so that loose fingers were less likely to get nipped. ASIDE: Audio devices held on to incandescent lamps (With specific referenc e to the 47) well into the 80s, before shifting - very slowly - to LEDs or Fluorescent lamps. But, they had transformers on board to isolate the chass is.

It is designed to operate at ~120V AC. It _CAN_ operate at ~120V DC, but on ly one post will light. It will trip (glow) at about 90V +/-.

Unless there is a voltage dropper in the circuit, it will fail quickly at 2

20 or 240 V - that is voltages outside of Japan and the Americas. As suppl ied, it has a 100K resistor in series with the lamp. For conversion to 220V , I have heard values of up to an *additional* 220K in series. Try there an d work back if you wish to operate at 220V.

As about 2/3 of my hobby time is dedicated to vintage radios, I am quite fa miliar with, and keep a bunch of these lamps in my spares-box.

Peter Wieck Melrose Park, PA

It will fail immediately without a series resistor. As others have said, there is no resistor built into the lamp.

From a 1965 Allied Radio catalog, Chicago Miniature lamp: NE-51 is clear glass tubular, single contact bayonet base. Voltage across the lamp is 65V when operating at the rated 1/25 watt.

A higher voltage is necessary to ionize the neon (which is why a relaxation oscillator works). The voltage is somewhat constant with varying current. At 1/25 watt and 65 volts the current would be 0.6 mA and the series resistor for 120V supply would be 91k (minimum).

There is also a NE-51H that runs at a blinding 1/7 watt (2 mA).

Nice case. How old is that thing? What's inside?