issue when trying to drop the voltage on the pulse out from a dekatron

[cjk...@hotmail.com]

I bought one of Threeneurons (mike?) dekatron spinner kits to play with some ideas. I'm new tubes in general. Anyway, the dekatron puts out about a 50-60 volt "pulse" at NDX. I am trying to drop that closer to 5v but at least less than 10v. I tried using a voltage divider made of 2 resistor going from the NDX output to ground but this stops the dekatron movement. Can anyone offer some advice.

 

BTW I am powering this from a +12/-12 DC power supply using +12 and ground. I'm not using the -12. Not sure if it can be useful in any way but I thought I'd mention it.

[David Forbes]

What resistor values did you use? The circuit is high impedance, so you may
have reduced the pulse size enough to break it by loading it with your resistor
divider.

Try with a 1 megohm resistor to the dekatron and a 100k to ground. The pulse
will not be sharp, but it ought to be there.

The output of that divider will need to go into a CMOS device so as to not load
down the divider.


--
David Forbes, Tucson, AZ

[Charles MacDonald]

On 12-06-22 06:23 PM, David Forbes wrote:
> On 6/22/2012 2:52 PM, cjk...@hotmail.com wrote:
>> I bought one of Threeneurons (mike?) dekatron spinner kits to play with
>> some ideas. I'm new tubes in general. Anyway, the dekatron puts out
>> about a
>> 50-60 volt "pulse" at NDX. I am trying to drop that closer to 5v but at
>> least less than 10v.
>>

> The circuit is high impedance, so you
> may have reduced the pulse size enough to break it by loading it with
> your resistor divider.

> The output of that divider will need to go into a CMOS device so as to
> not load down the divider.

if course old tube guys think of a "Cathode Follower" type of circuit
for something like this. Just about any small triode would be able to
pick off the signal and give a small voltage output. Lots of low price
COMPACTRONS out there.

--
Charles MacDonald Stittsville Ontario
cm...@zeusprune.ca Just Beyond the Fringe
http://users.trytel.com/~cmacd/tubes.html
No Microsoft Products were used in sending this e-mail.

[cjk...@hotmail.com]

On Jun 22, 4:23 pm, David Forbes <dfor...@dakotacom.net> wrote:

Thanks! this worked on the lower speeds but was still freezing at
higher speeds until I adjusted the PW resistor in the neon relazation
oscillator and now all works as I'd like it to.

[threeneurons]

On Friday, June 22, 2012 2:52:34 PM UTC-7, cjk...@hotmail.com wrote:

I bought one of Threeneurons (mike?) dekatron spinner kits to play with some ideas. I'm new tubes in general. Anyway, the dekatron puts out about a 50-60 volt "pulse" at NDX. I am trying to drop that closer to 5v but at least less than 10v. I tried using a voltage divider made of 2 resistor going from the NDX output to ground but this stops the dekatron movement. Can anyone offer some advice.

 

The pulse isn't 50V. Its limited by the little LED to whatever the forward drop of that LED is. ~2V (but biased 50V above ground; 50V to 52V). All the cathodes, are biased 50V above ground, and that's what you're seeing on your voltmeter.  If you want to interface it to some other circuit, try using an optocoupler:

http://www.allelectronics.com/make-a-store/item/4N33/OPTOISOLATOR-DARLINGTON-OUTPUT/1.html

http://www.vishay.com/docs/81865/4n32.pdf

Replace the current LED with the diode leg of the optocoupler. On the other side you have an electrically isolated darlington transistor (if you use the one above). Connect its collector to your low voltage logic supply. Connect the emitter to a resistor (between 2.2K and 10K), and ground the other leg of resistor. You should get a pulse off that emitter. 

A warning about optocouplers, they have a spec called current transfer ratio. For a regular transistor type, that could be between 20% to 50%. For darlington types is over 100%. The spinner current will only be ~300uA. If you use a regular transistor type, the output current will be only 60 to 150uA. To see 5V across a resistor, the resistor needs to be at least 82K. That's kinda high, unless you're interfacing to 4000 CMOS.