[sdiy] the function of neon lamps?

[Scott Gravenhorst]

John P <johnp299792 at ameritech.net> wrote:
>Yeah, they're used as oscillators.
>My mother has had a Lowrey (?) organ for about 30 years...  open it up, 
>lots of little neon lamps inside.
>Just beware of the p-p voltage when you're playing with them though - I 
>think they're close to household voltage! (~100V).
>
>I don't remember offhand *how* they oscillate... it's possible that 
>they're natural sawtooth generators in that they'll build up a charge to 
>the point where they emit light, then the charge goes to zero.

They are "sawtooth" oscillators, they work much the same as an avalanche
diode oscillator, current is fed through a resistor from the supply to a
parallel system of a capacitor and a neon bulb.  The neon bulb has a
threshhold voltage (NE-2 bulbs are around 65 volts) at which point the
bulb conducts (and lights) discharging the capacitor and restarting the
cycle.  These oscillators are not very stable.  They are affected by light
in the environment (so they need to be in a dark enclosure).  Some neon
bulbs have a tiny bit of radioactive material inside them to help
stabilize them.  I put sawtooth in quotes because charging a capacitor
through a resistor (the most common way for a neon oscillator) does not
yield a linear ramp as we have in out modern synth circuits, rather it's a
curve which climbs most rapidly from zero volts.

Another thing that neons can be used for in an organ is a frequency
divider.  Using a specialized version of the neon oscillator employing two
series neon bulbs and a properly adjusted current feed resistor, it's
possible to synchronize the special oscillator so that it fires once for
every two input pulses it receives.  This creates a pitch exactly one
octave below the input (very useful!).  I have a schematic for this, I got
it from someone on this list (thank you - whoever that was) and I can send
it to you if you're interested.


>Antti Pitkämäki wrote:
>
>> Hi!
>>
>> Could somebody please explain me what is the function of neon lamps? I 
>> know what transistors do, and I know what triode tubes do, but I 
>> really don't know exactly what neon lamps do (except create light!). I 
>> once read about "neon gas tubes" from some old electronics book, but 
>> unfortunately this book is not available in the library of the city 
>> where I live, so I can't find this information from anywhere...
>>
>> I'm interested in this subject because I have two Philicorda organs 
>> that have over 100 neon lamps inside them. Also I heard of a Lowrey 
>> tube organ that had over 1000 neon lamps inside (+64 tubes). Also I've 
>> heard that neon lamps can be used to build oscillators etc. Isn't the 
>> Bird organ based completely on neons except for amplification? Somehow 
>> to me, maybe partly because I was born in the early 80's, all these 
>> glowing tubes and neons seem much more "space age" and "science 
>> fiction" to me than boring old transistors and microchips ;)
>>
>> Thanks in advance,
>> Antti Pitkämäki
>>
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>
>-- 
>m/n/m/l
>surreal electronic music, sound, noise
>http://mnml.soulcatcher.net
>
>

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