A-108 Dekatron circuits?

[William Lee]

Hi all-

 

Besides the OG-4s I got in for threeneuron's great dekatron spinner kit, I also recently picked up a few A-108s.  The extremely small size appealed to me for whatever reason.  I've been perusing the VTA entry on them, and see that they count base 5 instead of 10, but was wondering if anyone had any sample circuits for them or feedback on projects that they've used them in.  If the Yilane kits were still available, I would definitely grab one of those, but it looks like I'm on my own as far as building a board with these.  Any suggestions or comments would be appreciated.

 

Thanks,
Dylan

[Tidak Ada]

In case you make adapters for different dekatrons to the octal socket and eventually make R7 and R10 switchable for higher supply voltages, you can make a dekatron tester with the print. Don't forget to adapt the diodes D1-3 and capacitors C2-4 to the higher voltages. Some suggestions Mike already gave in this [  Re: FS: Shameless Plug Time - Dekatron Spinner Kits ] thread on my question about using a ELESTA EZ10B high speed dekatron. This tube needs a supply voltage of at least 500V.

Warning: Remember, 1/4 W resistors are rated for only 200V working voltage, so look for >400V replacements for R 7 and R10-11 !! Also power ratings of some resistors ask for adaptation to 1/2 or 1W types.

See further the thread:  (Re:) FS: Shameless Plug Time - Dekatron Spinner Kits

 

Have interest in the A108 dekatrons, the datasheet in particular !

 

eric

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From: neoni...@googlegroups.com [mailto:neoni...@googlegroups.com] On Behalf Of William Lee
Sent: donderdag 2 februari 2012 19:34
To: neoni...@googlegroups.com
Subject: [neonixie-l] A-108 Dekatron circuits?

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[threeneurons]

> In case you make adapters for different dekatrons to the octal socket and
> eventually make R7 and R10 switchable for higher supply voltages, you can
> make a dekatron tester with the print. Don't forget to adapt the diodes D1-3
> and capacitors C2-4 to the higher voltages. Some suggestions Mike already

I was looking at the A108 data, and its description from the TCA
sight. This is an odd animal, which, depending on hook-up, may, or may
not, work with standard guide pulsing. The only way to find out is to
actually run tests on a real tube.

[dr pepper]

I like the bent over electrode appearance of the a 108.
I looked at a russian datasheet for it and it doesnt show any guide
electrodes, it shows it as having 10 cathodes and 1 anode, no other
connections.
Its shown as having all the even cathodes connected together to the Q
of a flip flop, and all the odd to not Q, looks like when you toggle
the flip flop the arc jumps to the next electrode, implying only 1
direction is possible, maybe thats why the electrodes are angled over
to ensure transfer direction.

[Tidak Ada]

Hmm, so it would be easier to use a usual 10-counting dekatron as a
5-counter by circuit design ??

[e]

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[threeneurons]

> Hmm, so it would be easier to use a usual 10-counting dekatron as a
> 5-counter by circuit design ??
>

Don't know, until I fire one up. Its possible that it could be stepped
just like a EZ10B, but I'm not sure of the proper bias and pulse
levels.

From what I've read, its count direction is due to the electrode
shape. Same as the EZ10 and WE 6167. The G10/241 nomotron direction is
determined by the cathodes being made of two types of metal, instead
of the shape. All have a single guide set. The A108 also has another
mode were the odd and even cathodes are bounced out of phase. Its one
strange little tube.

[threeneurons]

> Don't know, until I fire one up.

Can't fire one up, if I can't get one. None on eBay, nor the Russian
tube stores I'm aware of. Jan & Walter don't have them either. Anyone
got one to sell, or trade ? Contact me at my personal email, if you
do.

Thanx

[threeneurons]

David Blevins let me borrow his A108. He loaned it to me months ago, and I finally got around to playing with it. It ends up being a very forgiving tube. I've gotten it to work, with a supply voltage as low as 250V. It may even go lower. I started my tests using a 450V supply. That means it will work with 330V, which you'll get from simply rectifying and filtering 220VAC, or a simple doubler circuit on 120VAC. I tried 4 different spinner setups. The simplest using a 555, with a single HV transistor. Here is the link to my findings:

http://threeneurons.wordpress.com/dekatron-stuff/auxiliary-dekatron-stuff/

The related info is at the very bottom.

Here is the 555 spinner circuit:

You can use a flip-flop with the KE and KO set alternating, but it really is unnecessary. Have Fun, if you can find one of these tubes ! 

[Dekatron42]

The A-107, 8, 9 & 10 are base 10 Dekatrons just like any other Dekatron, you will however have to use an output stage (or more) to use as a counting output - otherwise you will just have a divide by 2 circuit from the flip-flop itself. The output stages can be connected together in a wire-or setup, with a proper reset/set stage you can then divide with any number you want (although probably with some reduced speed if you don't wire the circuit properly).

 

The datasheet shows a transistor and resistor in one of the cathode circuits which is used as the output stage. You can also reset/set them to any position by using a diode in the same fashion as with other Dekatrons, the diode is used to protect the counting circuit from the negative pulse used for resetting/setting - this is also shown in the datasheet.

 

If you use one output stage in each cathode circuit you can use them to drive a Nixie too, doing so will affect the counting speed somewhat but can mostly be compensated by adding a capacitor across the resistor in the cathode output circuit, much like it is done with the Elesta EZ10A/B Dekatrons. The flip-flop will have to be designed so that it will work properly when the extra current from the Nixie flows through the flip flop transistors as well as through the output transistor, this will probably mean that you will have to use a "proper" biasing network with a diode connected to the bias voltage and not just a resistive voltage divider. Or you can just add some extra transistors (similar to a darlington transistor) to the output stage which means that the current needed to switch on the output transistor is negligible in the flip-flop circuit and the Nixie current is routed through another transistor not flowing through the flip-flop.

 

Adding an output transistor requires that the voltage across the output transistor as well as the flip-flop transistor is choosen correctly so that they don't upset the Dekatron voltages nor the bias voltage when they switch.

 

I have done some experimenting with this and have slow counting circuits driving Nixies working as well as I can get them to do, but getting them to work at higher speeds is almost impossible when working on a prototype board. I guess that I will have to solder the components directly to teh sockets to shorten the wires and lowering capacitances/inductances in the circuits. Cramming transistors and all stuff into the small space under the small sockets is quite fiddly.

 

/Martin

[threeneurons]

Martin,

Do have a link to that document. Are they driving the nixies directly, or thru transistor buffers ?

Here's a little more complicated "selector" circuit, I made:

And here's a video of it working:

http://www.dailymotion.com/video/x129my8_a108-selector-demo_tech

Damn thing is a pretty simplistic tube ! Even simpler than a standard dekatron ! But it does function nicely.

[Dekatron42]

Nice circuit! I really like it and I will certainly save it for the future!

 

I was planning on using high voltage opto-couplers like MOC8204 or HSR412 instead of the white LEDs you are using to drive a Nixie.

 

With the original circuit in the datasheet they usually only use the outputs for output to the next stage, sometimes with wire-or for more complex output signals, for driving Nixies they hook up more transistors as buffers or cold cathode trigger tubes to drive the Nixies.

 

If you want to divide by anything else than 10 your circuit will have to make sure that it sets (or resets) the flip-flop to the correct position just before the reset pulse is applied to cathode 0, otherwise the cathode will not light up and stay lit since the flip-flop transistor for the even cathodes is not conducting and no current will flow through the "even" transistor to ground keeping the 0 cathode lit. The same kind of situation applies to the Burroughs Beam Switching tubes if you want them to count to anything except 10 (or to a number that is not possible to apply by joining the correct spade or target electrodes) as the flip-flop driving the odd and even electrodes will be in the wrong position for the beam to form. If you want to set the A-108 to any other number you will likewise have to make sure that the flip-flop is set to the odd or even state that matches the cathode that you are setting it too.

 

When I experimented with them I made a flip-flop of low voltage transistors and used KSP44's as buffers and I also added the set/reset logic via a rotary switch with two wafers, one for set/reset to the flip-flop and one for selecting what cathode I wanted to set, with a delay circuit to make sure that the flip flop had changed state before the set pulse was applied, this was the easiest way I could think of then without involving a lot of more transistors. I was building a small clock without any IC's so I wanted to keep it small and simple but I really wanted to use the set capability of the Dekatron and not just use a pulse to count up to the correct number. I also experimented with blanking either the Nixie or the Dekatron just as the set procedure was performed as the Dekatron will count one step forward as the flip-flop is changed (if it is changed) and that did not look that nice I think, the dekatron will count one step forward if the flip-flop changes states just before the set pulse is applied to the cathode if you go from an odd number to an even number or vice versa.

 

I think that these small Dekatrons are the most beautiful design, and as you say simplistic, that I have ever seen. They are very forgiving when it comes to voltages and as you have shown here they are quite easy to hook up and get to work properly. The A-107 and A-109 are equally easy to get to run, but as soon as you want to use any of them at higher frequencies you will have to be careful when designing the circuit properly, just as with any other high speed dekatron.

 

/Martin