Can you folks take a quick peek at my schematic for Classic Rev6?

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7 months 1 week ago #11873 by Ty_Eeberfest
Yea I'm confused now too. Seems like it shouldn't be able to work because a neon lamp is essentially an open circuit until it strikes. I may set up a little test myself tonight or over the weekend.

Meanwhile, Ian would you care to comment??

Look into it later when the dust is clearing off the crater.

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7 months 1 week ago #11874 by Ty_Eeberfest
Okay here is what I found:

I set up a test using a 170VDC supply (real power supply, not just wires scabbed on to a clock). To validate the power supply I checked output with a meter (170V) and then used it to light a single neon with a 120K resistor (good - no discernible flicker).

With 2 brand new neons in series + a 120K resistor I must admit they did light up. However, operation was not what I would call stable. One was always "brighter" (more of the cathode covered in glow) than the other - this can be explained by the fact that no 2 neon bulbs are perfectly identical. Both bulbs were visibly flickery like neons will flicker when they are right on the edge of their extinction voltage.

What's happening is that the leakage through the unlit neons is being exploited to get 2 in series to light at all. I'd throw it into the same category as when you take advantage of a software bug to make something work. I would not do it but it's your project. I already told you how I would do it if it was my project. I don't know why you wouldn't want to do it that way since its only a couple resistors more.

Look into it later when the dust is clearing off the crater.

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7 months 1 week ago #11875 by Torsten Lang
I would strongly advise NOT to connect the neons in series. The Blue Dream clock has this design flaw and the neons repeatedly failed after some time of ageing when striking voltage increases.

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7 months 1 week ago #11876 by ironspider
Thank you both for taking the time to help walk me through this! And I think it's finally starting to click with me how I initially read that page in the manual incorrectly and Ty, what you're saying about the exploiting the situation--that makes sense. And Torsten I think I now get what you're saying in that as the neons age the striking voltage will increase which will eventually get into a situation where the voltage being halved (via series wiring) won't be enough to ignite the neons?

So, just so I'm clear, the wiring should be:
1. HV from SV1 to a leg of each of the two neons
2. Replace the resistor on the board at R19 with a jumper (effectively removing it)
3. Put 2 appropriate resistors (somewhere in the 120k-270k range) on the other legs of the neons (1 per neon)
4. Run each of those legs back to SV2-"1"
5. Do the same for the other two neons (which can then be also run back to SV2-"1" or SV2-"2")

Do I have that correct?

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7 months 1 week ago - 7 months 1 week ago #11877 by Ty_Eeberfest
Voltage being halved is part of it but also there's the matter of an unlit neon being an extremely high - theoretically infinite but practically not quite infinite - resistance. Two "theoretical" neons in series would never light. Two real world neons in series will work, at least for a while, because of leakage in the unlit state. No telling how this leakage will change as the bulbs age.
(not quite right! see Torsten's post below)

Your description of connections has me confused. You said you are working with a Classic Rev. 6 clock. On the Rev. 6 board SV2 is the front panel connector. SV6 is the connector for LEDs, tick neons, etc. Pins 2 and 3 are the "ticks".

You are correct that R19 (and R22) should be eliminated: remove resistors, replace with jumpers. This is not essential but is just good / clean practice.

For the rest, I prefer pictures. Here's a sketch with the correct connector numbering.


Look into it later when the dust is clearing off the crater.
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Last edit: 7 months 1 week ago by Ty_Eeberfest. Reason: I misspoke!
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7 months 1 week ago - 7 months 1 week ago #11878 by Torsten Lang

Ty_Eeberfest wrote: Voltage being halved is part of it but also there's the matter of an unlit neon being an extremely high - theoretically infinite but practically not quite infinite - resistance. Two "theoretical" neons in series would never light.

Hello Ty,
you forget that the middle pin between the two neons in series HAS a potential. If the difference to the upper or lower voltage is higher than the ignition voltage current will start to flow in the corresponding neon until the difference is low enough again.

It doesn't differ basically from driving a single nixie with a driver like a 74141. Let's assume the driver is "off": When the potential on the cathode pin (connected to the open collector output of the IC) is higher than the breakdown voltage of the transistor the transistor will start to conduct until the voltage has dropped enough. On the other hand, when the potential goes down too much the tube will start to conduct. So there is a window where the potential (or voltage) on than "open" pin can reside without the transistor or the tube starting to conduct.

It's not any different for the tubes in series. The middle pins cannot have "no" potential...

Regards,
Torsten
Last edit: 7 months 1 week ago by Torsten Lang.
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