What kind of lamp is this?

lgreen · 20th July 2007, 08:15 PM

This is for an on/off light on an HP59500A and I'd like to light it up as i'm using the case for a preamp. But I don't know if its AC or DC or what??

thanks!

Duo · 20th July 2007, 08:23 PM

That is a neon indicator lamp in series with a resistor which is normally operated from the 120VAC line. Depending on the value of the resistor.

It looks like a 33K resistor, so it's not at all unlikely that it would be operated directly from the line. (Those lamps are normally around 60V operating voltage, and so you'd have 60V or so across the resistor and around 1.8mA which is fine for a neon lamp like that.)

lgreen · 20th July 2007, 08:56 PM

The resistor measures 31.6K.

So its a line-driven AC lamp huh?

Thanks a bunch, ok, now to see if the lamp still works.

Duo · 20th July 2007, 09:01 PM

Yeah, the lamp is simply a glass bulb filled with low pressure neon gas with two metal rods inside.

The 120V line is of enough voltage to cause ionization of the gas inside. Once this happens, the lamp conducts an electrical current and exhibits what's known as negative resistance. It will conduct current as if a near short until the voltage reaches its rated operating voltage (set by the gas type and the distance between electrodes).

They're really very neat in principle. You can make oscillators with them

Just takes a cap, a resistor, and a neon bulb to make such an oscillator.

Anyway, enough of all that theory, just wire it up safely and it should illuminate as long as it's not too old. (They do get dim/weak with age and eventually don't strike anymore.)

lgreen · 20th July 2007, 11:31 PM

Well the lamp works but only at 125V. I was unable to get it to turn on with the unit plugged into the wall, but was able to get it to turn on using the VARIAC. ....and found that it needs about 125V to glow its yellow glow.

Gonna either have to replace the resistor or lamp?

Duo · 20th July 2007, 11:38 PM

The lamp's probably very old, hence the darkness of the glass. What this means is that the impurities in the gas are having their effect over time as the lamp was used and has aged.

You would want to replace the lamp. Your measurement shows that the resistor is fine.

Those lamps can be found all over the place, you just have to look.

20th July 2007, 08:56 PM	#3
lgreen diyAudio Member Join Date: May 2003 Location: San Diego, USA	resistor The resistor measures 31.6K. So its a line-driven AC lamp huh? Thanks a bunch, ok, now to see if the lamp still works. __________________ My DIY audio projects- PartTimeProjects.com.

20th July 2007, 11:31 PM	#5
lgreen diyAudio Member Join Date: May 2003 Location: San Diego, USA	works kinda Well the lamp works but only at 125V. I was unable to get it to turn on with the unit plugged into the wall, but was able to get it to turn on using the VARIAC. ....and found that it needs about 125V to glow its yellow glow. Gonna either have to replace the resistor or lamp? __________________ My DIY audio projects- PartTimeProjects.com.

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20th July 2007, 08:23 PM	#2
Duo diyAudio Member Join Date: Jun 2002 Location: Victoria, BC, Canada	That is a neon indicator lamp in series with a resistor which is normally operated from the 120VAC line. Depending on the value of the resistor. It looks like a 33K resistor, so it's not at all unlikely that it would be operated directly from the line. (Those lamps are normally around 60V operating voltage, and so you'd have 60V or so across the resistor and around 1.8mA which is fine for a neon lamp like that.)

20th July 2007, 09:01 PM	#4
Duo diyAudio Member Join Date: Jun 2002 Location: Victoria, BC, Canada	Yeah, the lamp is simply a glass bulb filled with low pressure neon gas with two metal rods inside. The 120V line is of enough voltage to cause ionization of the gas inside. Once this happens, the lamp conducts an electrical current and exhibits what's known as negative resistance. It will conduct current as if a near short until the voltage reaches its rated operating voltage (set by the gas type and the distance between electrodes). They're really very neat in principle. You can make oscillators with them Just takes a cap, a resistor, and a neon bulb to make such an oscillator. Anyway, enough of all that theory, just wire it up safely and it should illuminate as long as it's not too old. (They do get dim/weak with age and eventually don't strike anymore.)

20th July 2007, 11:38 PM	#6
Duo diyAudio Member Join Date: Jun 2002 Location: Victoria, BC, Canada	The lamp's probably very old, hence the darkness of the glass. What this means is that the impurities in the gas are having their effect over time as the lamp was used and has aged. You would want to replace the lamp. Your measurement shows that the resistor is fine. Those lamps can be found all over the place, you just have to look.

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