The problem with Neon..

[CJ]

edited drunken post yesteryear  :-\

isn't there a neon in the LA2a?

they can get noisy if they "sputter" from lack of current, or when they get old,

 

[benb]

I'm surprised there's not a more detailed description of how these little neon bulbs work. Yes, they can be used with DC as voltage regulators, but that put them into continuous conduction where they don't make (as much) noise. They're not used that way for power-on indicators used in and near on-off switches.

The neon bulb looks like an open circuit (no current flows) until the voltage between its terminals reaches around 80 volts, the firing voltage. Then it suddenly turns on and starts conducting. For 120VAC operation they have a resistor in series, I think around 50k ohms. As soon as it conducts, the voltage across the bulb drops back suddenly to 60 or 70 volts, and stays there until the voltage drops to below this running voltage (by the voltage on the other side of the resistor dropping below this 60 to 70 volts).  This voltage change at firing is high speed and generates a pulse into the RF range. You can probably put an AM radio near a neon bulb power indicator and pick up the 120Hz buzz. The saving grace is the wire between the resistor and the bulb is an inch or so long, so the turn-on pulse isn't that great in intensity and doesn't travel far. It's not a huge source of electrical noise, but it's enough that for good performance you want to double-check that having it powered by the AC line doesn't add to buzz or noise in equipment.

Large neon signs (that use those large and deadly 5kV to 10kV transformers) work the exact same way, but with longer wires, higher voltage and higher current, so the chance for and volume of interference is much greater.

I once bough a Dual 1229 turntable used. I noticed the "strobe" indicator didn't work, and I found the wires going to the neon bulb that shines its light on the strobe were cut. I figured this was for good reason (the previous owner might have noticed a buzz until cutting the wires), so I wired a switch so I could turn it on and off. I only need the strobe on when checking platter speed, not when playing a record.

 

[JW]

Ugggg,

So, I have like 7 pieces of gear that I built with frikking Neon 120V bulbs, just like in the picture on page one.  Power supply units, compressors, eq's, what have you's.

Anyway, is there an elegant solution for using the 120V ac and even perhaps the plastic casing of the Neons that I already have in there?  I'd sort of like to do a global swap on all my stuff with Neons. . . . .

 

[abbey road d enfer]

Ugggg,

So, I have like 7 pieces of gear that I built with frikking Neon 120V bulbs, just like in the picture on page one.  Power supply units, compressors, eq's, what have you's.

Anyway, is there an elegant solution for using the 120V ac and even perhaps the plastic casing of the Neons that I already have in there?  I'd sort of like to do a global swap on all my stuff with Neons. . . . .

You could probably run them from rectified/filtered voltage; then the main source of interference (the recurring striking/discharge) would disappear. The series resistor should be increased in accordance with the increase in voltage resulting from rectification.

 

[JW]

Cool.

So, for an example, here's a pretty common power supply folks use around here and which I have in a couple pieces of gear. The mnats little PSU:  http://mnats.net/psu.html 

Are you talking about using a series resistor connected to where the diode bridge (D2)  connects to C1?  Where would I then connect the return from the Neon bulb? And how would I calculate the value of the resistor?

 

[abbey road d enfer]

Cool.

So, for an example, here's a pretty common power supply folks use around here and which I have in a couple pieces of gear. The mnats little PSU:  http://mnats.net/psu.html 

Naaah. See attachment.
Just make sure that your wiring is properly insulated since it is connected directly to mains. Usually, the insulation of the switches is rated for direct power from mains, so that shouldn't be an issue.

 

[Gene Pink]

Naaah. See attachment.
Just make sure that your wiring is properly insulated since it is connected directly to mains. Usually, the insulation of the switches is rated for direct power from mains, so that shouldn't be an issue.

There ya go. But I would ditch the 1K, replace the fuse with the 100K, so 100K >  bridge (or just one diode) > cap > neon. Two added parts beyond an AC neon.

The tube guys here are doing DC for filaments in the quest for lowest noise, so why not DC neons?

The only problem, neon on AC:

 

[Gene Pink]

And neon on DC, only the negative side glows. Might matter, might not:

 

[abbey road d enfer]

But I would ditch the 1K, replace the fuse with the 100K, so 100K >  bridge (or just one diode) > cap > neon. Two added parts beyond an AC neon.

Congrats! You're cheaper than me..

 

[Gene Pink]

Congrats! You're cheaper than me.. [/quote]

Hey, now.

I resemble that remark.
;-)

(this post has no attachments, if there are, don't click.)

 

[JW]

Thanks guys!

Sorry for my ignorance here, but just to absolutely verify, this whole circuit is tapped off the mains and running parallel to the existing power supply?

i.e. This is a separate set of rectifier diodes (or one as mentioned) and I shouldn't be interpreting that it starts running parallel after the the already existing rectification?

And by the way, how am I supposed to use one diode if there's 4 connections, or are we talking about those 4 in 1 diode packages?

Thanks for the help. This is really handy that I don't have to drill new holes for a different bulb or some other cosmetic problem.

 

[abbey road d enfer]

Thanks guys!

Sorry for my ignorance here, but just to absolutely verify, this whole circuit is tapped off the mains and running parallel to the existing power supply?

i.e. This is a separate set of rectifier diodes (or one as mentioned) and I shouldn't be interpreting that it starts running parallel after the the already existing rectification?

Yes.

And by the way, how am I supposed to use one diode if there's 4 connections, or are we talking about those 4 in 1 diode packages?

See attached dwg

 

[JW]

Hmmmm? dwg?

Did it not attach?

 

[JW]

Oops,

Disregard that last post. I checked back again (a LONG TIME later,) and there it is.

Just one more question though about that last drawing. Is that a polarized capacitor? Also, that is another resistor after the cap right? 100K?

 

[abbey road d enfer]

Oops,

Disregard that last post. I checked back again (a LONG TIME later,) and there it is.

Just one more question though about that last drawing. Is that a polarized capacitor? Also, that is another resistor after the cap right? 100K?

The first resistor is there to reduce the current surge when powering, the second one is there to limit the current through the neon bulb; 100k is a good start, then adjust to taste if you want more/less illumination.

 

[JW]

Thanks Abbey!

Sorry to nitpick but this is AC mains we're dealing with. Is it necessary for that cap to be polarized? I tried looking up capacitor markings like you're drawing and I can't find anything that looks exactly like that.

 

[abbey road d enfer]

Thanks Abbey!

Sorry to nitpick but this is AC mains we're dealing with. Is it necessary for that cap to be polarized? I tried looking up capacitor markings like you're drawing and I can't find anything that looks exactly like that.

The cap can be anything from 1 to 10 uF, so it may be film cap or a lytic; in the latter case you must connect the positive side to the diode's cathode.

 

[JW]

Okay

So . . . finally got around to trying the DC neon using schematic Abbey posted five posts ago.

I'm getting some pulsing from the neon on startup. After about 2 or 3 seconds it stops and stays solid. Would this be normal in this circumstance?

Of note:  I adjusted the second resistor to 1K for (a tiny bit) more light. It was pulsing with the 100K in there too though.

 

[abbey road d enfer]

Okay

So . . . finally got around to trying the DC neon using schematic Abbey posted five posts ago.

I'm getting some pulsing from the neon on startup. After about 2 or 3 seconds it stops and stays solid. Would this be normal in this circumstance?

Of note:  I adjusted the second resistor to 1K for (a tiny bit) more light. It was pulsing with the 100K in there too though.

What value is the first resistor? It should be smaller than the second one. It is normal to have pulses during the voltage ramp-up, but it should be unnoticeable. Making the 1st resistor much smaller than the second should make it invisible. If it persists, you may reduce the value of the capacitor.

 

[PRR]

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