Question on neon bulbs for circuit

[Dylan Distasio]

Hi all-

I'm interested in toying around with some circuits based on neon bulbs.  I have a question for anyone who knows these well.  Can I substitute a NE-2E (A9A) for a NE-2 (A1A) in my counting circuits without an issue?  The only difference I can see is the current ratings.  I'm asking because I can get the A9As for significantly less money and would like to go that route if they will work.

Thanks,
Dylan

[threeneurons]

Depends how you're using those neons.

If its for display only, then it really doesn't matter. Yeah, one may be rated to use different current levels, but it will still function. Life may be the only issue.

If you want to try some neon logic circuits, where the NE2s are intended to be the actual logic elements, then the bulb type is very important. Little NE2s of any type are going to be a pain, and its going to be hard to get any circuit working. Usually, other bulb numbers are specified. Your typical NE2 does not have a specific anode or cathode. For logic circuits, bulbs that do, seem to work better. The key for reliable neon logic operation, is the difference between strike, and maintaining voltage. The bigger the better. That is a bulb with 100V/60V strike/sustain specs will do better than one with 75V/65V rating.

On top of that, once you get your neons, you'll have to age them. That is run them at a higher than normal current level, for a day or two. After aging them, you'll then have to 'batch' them. Take each bulb, and measure its strike, and maintenance (sustain) voltage, and put them in separate cups with other bulbs that match. 'Match' means no more than 2V difference from the other bulbs. This aging and batching procedure is key to a successful operating circuit.

Modern circuitry is much less a pain, than some of those circuits encountered in the old days. I remember growing up, and trying out circuits from Popular Electronics. Many I could never get to work. They required tweaking, and prep-work. I usually went straight to the schematic,and MAYBE, only read the text, afterwards.

[NoCampersFluffy]

Hello

Specs for both are close A9A 0.7ma vs A1A 0.6.  However,
http://www.donsbulbs.com/cgi-bin/r/b.pl/neon|ne2~usa.html
lists the following:
DC breakdown volts:70avg
DC maintain volts:59avg
after 100 hours at design current
design current/MA:0.3
end of life is 5v change in breakdown for maintaining voltage
maximum diameter:0.275inchs
neon glow lamp
pre-aged:no
voltage range:105-125v

If this website data is true then there is only on average 11v differential between strike and maintain.  This will make it difficult for you to build a reliable circuit as you will be aiming at the mid point which is only 5.5v.

I've used IN-3's as they are cheep and have a good strike to maintain voltage differential (25-30V) - so you can design your circuits for the average point of 12-15v.    As threeneurons points out this your major selection criteria for neon bulbs in logic circuits.

Also remember that burning in bulbs with defined anode/cathode is different to burning in bulbs without a specific anode/cathode designation.  The bulb types without a specific anode/cathode designation can become fixed after burn in. I have not seen this myself as I've only used IN-3s, which have a defined anode/cathode, but the literature talks about burn in memory for bulbs. This is important for bulbs like NE's as you must remember which way to place them in circuit after burn in. Whereas the IN-3's have a little arrow in the glass.

I've found that an aged lot of 400 bulbs is enough to find enough batches of bulbs with the same characteristics to build a clock. Tighter batching will give better circuit performance, particularly for those circuits that are only triggered periodically such as minute and hours ring circuits in clocks.

I've found no real issue with circuits from 100HZ down to 1/10hz, although I have not experimented with higher frequency circuits.

If you are looking for reliability then you will find that over time, once reliable circuits for minutes and hours become unreliable and require bulb reorganisation or replacement - good to have lots of spares in your matched batches.  Reliability goes down with the time a bulb is switched off even though I have supplementary lighting to assist ignition. So far I have not been able to find the compromise lighting level required to display the circuit under Perspex in my office without closing the blinds to keep all sunlight out. Intermittent errors occur as the strike point of some bulbs in the circuits is lowered by stray light.

Hope this helps

[Joe Croft]

Hi Dylan,

I have had little issues with the A9A bulbs and I have done a lot of counting circuits. Of course, I suspect that any type 2 terminal neon bulbs will cause you grief if you want good reliability. I've tried aging them and that didn't seem to help. Matching the bulbs seemed to work the best, though if you get reasonably new bulbs (since the date of mfg) they are pretty (though not 100%) pretty close and you can match them as you build the counter.

-joe

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