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ianl 10th March 2006 12:33 PM

New member introduction & question
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I am a new member from the Netherlands. I have been lurking and reading the forum for a while now. I started working with tubes a few months ago. I made a few 'sculptures' with nixie tubes, and even designed my own SMPS.

After I became familiar with high voltage it occurred to me that it might be fun to play with other types of tubes. Several members of the NEONIXIE list (great group!) on yahoo highly recommended this forum.

This weekend I went to the tube shop and found some tubes to 'play with'. I got some ECC81 (12AT7), and EL90 (6AQ5A). I also found some small JAN6418 marked as low voltage tubes.

When I got home I googled the 6418 and found
this kit that uses the tube. It looked like a simple place to start and I had all the parts on hand.

I bread-boarded the circuit (just the pre-amp part), but realized that some of the connections were really blurry. Attached is a picture of the circuit. I enhanced some of the connections that were blurry, but obvious (to me). Can someone suggest what might connect to the points circled in red? It's probably really obvious to anyone with experience, but it has me stumped.

The red circle at the top is a 'supply line to nowhere'. The circle at the bottom is a junction with no attachment.

Thank you,


ErikdeBest 10th March 2006 01:22 PM

Hi Ian, and welcome to the forum

About the upper circle...I can only imagine this connection goed to a capacitor (maybe a bleeding resistor) with the other side connected to ground. The line in the lower circle stands for the connection of the outer side of the RCA output to ground: isolate the RCA plug from the chassis and use a piece of wire to connect the 'buitenkant' (outer side) of the RCA female plug to the central ground in the amplifier.


lndm 10th March 2006 08:20 PM

I am not quite certain what you are asking, and I cannot seem to access the jpg link you provided, but it seems you need a power supply.

Designing complete power supplies is probably too much to go into here but there is plenty of information on the web, and I see you have had experience with power supplies.

Do you have the TDSL from ? this is an easy way to find common operating points for common devices so you will know what power supply to aim for.

SHiFTY 10th March 2006 08:47 PM

That top circle would go to the other identical channel I think.

The bottom circle is just showing the connection from signal ground to chassis ground/power supply ground (0V)

anatech 10th March 2006 08:49 PM

The power supply indicated is 36 VDC. It will not fire a neon or nixie tube. It will run a fluorescent display like in the new consumer equipment (not LCD).


Riker 10th March 2006 10:22 PM

I'm having a problem creating a new thread that does not exist yet.

lndm 10th March 2006 10:41 PM

Tube index page, top right.

anatech 10th March 2006 10:42 PM

Hi Riker,
You should enable your e-mail in the use profile.

When starting a thread, search the topic, then check the "searched" box in the upper right corner of the page.


ianl 11th March 2006 05:45 PM

Thanks for the reply. I'm going to give the circuit a try now that I know I am not missing anything.

anatech: I dont know what you mean. I have a SMPS for nixie tubes - I'm going to 'dial it down' to power this circuit. I don't like the 555 circuit that they use - I have used those for nixies as well, but like my design better for various reasons (mostly familiarity).

When I get this pre-amp going, I will start to play with the resistor values to learn about bias et. al.



anatech 12th March 2006 12:35 AM

Hi Ian,
I was referring to the schematic you posted. The supply voltage is indicated at 36 VDC. That is below the ionization voltage for most gas discharge devices (neons, etc ...).

If you are going to hit the display with a higher voltage, then you are okay.


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