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Old 13th Apr 2015, 3:51 pm   #1
Dave Moll
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Default "beehive" neon lamp

Yesterday at Golborne, one of the stallholders gave me the neon lamp pictured below as a "freebie" with a purchase after I commented on having had one very similar as a nightlight when I was a child. As can be seen, it is missing its (presumably bayonet) fitting, so my question is whether such a lamp would originally have had a series resistor embedded within the cap, and if so, what value it is likely to have been.

I have been doing a bit of experimenting (that would have the H&S freaks tearing their hair out) and find that the highest value of series resistor which gives a reasonably stable and flicker-free glow is about 82K. The glow becomes increasingly intermittent as I increase the resistance beyond this. Measuring the voltage across this resistor with a DMM gives a reading of about 90V - which means the resistor must be dissipating a little over 1W (which is rather more than I would have hoped).
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Old 13th Apr 2015, 4:17 pm   #2
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Default Re: "beehive" neon lamp

Yes it would have had a built-in resistor. 90volts is about the maintaining voltage of a neon regulator so with an ac supply for a fair part of the cycle there will be no current as the instantaneous voltage will be less than that. This means that the power dissipation of 1W in the dropper, calculated from DMM readings could be high.
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Old 13th Apr 2015, 4:32 pm   #3
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Default Re: "beehive" neon lamp

A watt or so in a BC or ES cap wouldn't get that warm, if it were mine I would use a couple of 39k 1/2W resistors (both near the cap's edge) and stick an ES cap on it using silicone (ES, easier to get in and out of the lampholder).
 
Old 13th Apr 2015, 9:29 pm   #4
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Default Re: "beehive" neon lamp

These lamps have featured in a number of threads: search for "Osglim".

According to the catalogue extract in post #10 of this thread https://www.vintage-radio.net/forum/...d.php?t=100852 they were not available in ES cap.
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Old 13th Apr 2015, 10:20 pm   #5
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Default Re: "beehive" neon lamp

I realise that 'normal' neons need a series resistor to limit the current. Dave states that there is 90V across the 82k resistor that is in series with the lamp. That means there is already 150V across the lamp terminals. Maybe it is not a real neon and does not need a current limiting resistor.

The way to prove this is to reduce the series resistor in stages - say half for each iteration - and if the voltage across the resistor falls each time then you will eventually be able to prove if you can apply the full mains to the lamp.

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Old 13th Apr 2015, 10:21 pm   #6
Jeremy M0RVB
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Default Re: "beehive" neon lamp

Glad this one is in good hands. I have an Osglim of a completely different type - CV981 on a small screw base. The internals are very different and it's simply listed as a neon indicator. See http://www.tubecollector.org/cv981.htm - not clear in my pics it's clearly marked GEC and Osglim on one side and carries the old stores reference AP7469 on the other plus an anchor.
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Old 13th Apr 2015, 10:56 pm   #7
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Default Re: "beehive" neon lamp

@Alistair D: Have you ever actually encountered a gas discharge lamp that didn't need current limiting? I don't think such a thing exists as gas plasma always acts like a short circuit, but I'd like do be proven wrong.
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Old 14th Apr 2015, 5:18 am   #8
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Default Re: "beehive" neon lamp

I would not trust the DMM on a neon lamp resistor.
The lamp will act like a zena diode and will produce a waveform across the resistor that will confuse the DMM and give the wrong reading.
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Old 14th Apr 2015, 7:45 am   #9
Alan Stepney
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Default Re: "beehive" neon lamp

Those lamps originally had a BC base, and, from memory, they did have a resistor in the base. (A brown one with no markings or colour code, as far as I recal)

They were made up to the late 1940's, perhaps a few years later.

Yes, they are neon.
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Old 14th Apr 2015, 9:15 am   #10
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Default Re: "beehive" neon lamp

Here's mine: ex-BBC Valve Section. They were used as regulators in part of the Band I TV transmitter power supply at Kirk o' Shotts.

There was no resistor in the base.
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Old 14th Apr 2015, 9:32 am   #11
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Default Re: "beehive" neon lamp

It seems they were available with an ES base then, or were they only supplied to the BBC in that form? Both of mine are BC.

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Old 14th Apr 2015, 9:58 am   #12
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Default Re: "beehive" neon lamp

Quote:
Originally Posted by mark pirate View Post
'...were they only supplied to the BBC in that form? Both of mine are BC.'
No idea, but given the variations on neon and incandescent lamps back then, it would have been no problem to make them to a certain spec as per contract. I'm sure they'd be used for other contemporaneous industrial regulator circuits too.
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Old 14th Apr 2015, 10:09 am   #13
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Default Re: "beehive" neon lamp

Perhaps the resistorless ones were supplied in ES base to prevent accidental use in a lighting circuit. The Osram valve catalogue of 1938-9 lists several 300mA barretters with ES base for regulating heater chain current, but no resistorless Osglim.

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Old 14th Apr 2015, 10:56 am   #14
Alan Stepney
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Default Re: "beehive" neon lamp

In the 40's and 50's. it was rare if not unknown to have a mains socket that was ES as BC had been standard in the UK for many years.

The only ES I saw or have data on, was when it was used for valves, or similar electronic/industrial purposes.

If I am right, (and often I am not) then the ordinary household ones would have been BC, and any with an ES base for industry etc, and may well have had different characteristics in some way.
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Old 14th Apr 2015, 3:04 pm   #15
Alistair D
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Default Re: "beehive" neon lamp

Quote:
Originally Posted by Maarten View Post
@Alistair D: Have you ever actually encountered a gas discharge lamp that didn't need current limiting? I don't think such a thing exists as gas plasma always acts like a short circuit, but I'd like do be proven wrong.
Never seen one that doesn't need current limiting but I prefer to prove it rather than assume.

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Old 14th Apr 2015, 5:30 pm   #16
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Default Re: "beehive" neon lamp

AFAIK all common beehive neon lamps had a BC cap and an integral current limiting resistance for use on 200/250 volt AC mains.
The main applications being for nightlights or warning lamps when it was desired to use the lamp in a standard lampholder on a lighting circuit.

During the last war, some large air raid shelters had a neon beehive lamp located just inside the entrance. This served two purposes, firstly it helped those seeking shelter to find the shelter door in the blackout, but was not sufficiently bright as to attract the enemy. Secondly, the neon lamp lit the light switches whereby other, brighter lights could be turned on.
Certain types of very low output electric lamps, including beehive neons were approved for use in the blackout, provided that the lamp could not be directly viewed from the air. It was considered that a direct view of the lamp from the air was dangerous, but that a surface lit by the lamp was safe.

I would suggest that the ES cap beehive lamp without a series resistance was a special type not intended for general use.
As well as being used as a voltage regulator, a neon without a series resistance was also used as the light source in a stroboscope whereby moving machinery could be viewed as though it was stopped.
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Old 14th Apr 2015, 5:32 pm   #17
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Default Re: "beehive" neon lamp

Quote:
Originally Posted by Maarten View Post
@Alistair D: Have you ever actually encountered a gas discharge lamp that didn't need current limiting? I don't think such a thing exists as gas plasma always acts like a short circuit, but I'd like do be proven wrong.
Well, it doesn't act like a short-circuit (zero volts whatever the current), but it does have a negative incremental characteristic (voltage drop decreases as current increases), thus for stability, an external limiting impedance must be connected in series which is greater than this negative slope resistance.

Is there a gas discharge lamp that doesn't need current limiting? I've not heard of any either, though a gas discharge below the glow discharge point would be stable, although not producing much light! Think of a fluorescent lamp after switch-on, before the starter does its stuff - this would be stable without a limiting ballast (though it wouldn't be a good idea because a transient might cause the tube to strike, and then... bang!
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Old 14th Apr 2015, 5:54 pm   #18
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Default Re: "beehive" neon lamp

Neon lamps must have a resistor like any other gas discharge lamps.
The beehive lamp has a resistor in the base which was BC.
On DC you may want to reverse polarity,otherwise the disk would glow instead of the "beehive"
As for ES, this must be a special, Since BC was the standard in GB and over in some of the UK.
We are now seeing more ES lamps from the UK, (often 220v) getting to Britain,the problem with ES, they can work loose and then arc,if they are subjected to vibration,hence vehicle lamps are SBC.
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Old 14th Apr 2015, 6:09 pm   #19
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Default Re: "beehive" neon lamp

Quote:
On DC you may want to reverse polarity,otherwise the disk would glow instead of the "beehive"
Ah, the advantage of BC in this case.
 
Old 14th Apr 2015, 6:40 pm   #20
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Default Re: "beehive" neon lamp

These were often used by television experimenters in the early days. Television magazines of the 1930-35 era show how to warm the base in order to loosen the cement, prior to removing the resistor and re-fitting.

(Always mark the lamp clearly to avoid a mistake later)
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