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Old 3rd January 2006, 11:19 PM   #1
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Default Magic Eye spectrum analyzer

Im making a spectrum analyzer using 5 magic eye bargraph type tubes.


I want the system to run off of 6 or 12 volts. doesnt matter.

I did a search on this site, and found some stuff on magic eyes, but not sure how to go about wiring a bandpass filter up to them, because I dont think full-wave rectifiers will work, but I dunno.

Also, I googled, and found some steves pages, which had a small 3volt batter powerey amplifier, that uses a transistor, a gate oscillator, and an old filiment transformer as an inverter to supply B+ I was thinking of taking that approach

I got a chicago transformers 6.3v 2amp filiment transformer, and that might do the job.

Any tips, suggestions, comments, idea, schematics?
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Old 4th January 2006, 09:39 PM   #2
SHiFTY is offline SHiFTY  New Zealand
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To be honest it would be waaaay easier to use LEDs. To use tubes you will need a 250V DC supply and some pretty rare tubes.

If you are still keen google for the EM84, thats the tube you would want.
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Old 4th January 2006, 11:06 PM   #3
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I already got the tubes. And the parts to make an SMPS.

Ok, exactly how much current do I need to run a couple of these magic eyes?

I made a simple SMPS using a 555 timer, an NPN transistor, emitter resistor to burn off the current, and a filiment transformer.


I got 250 to 300 VAC output on the transformer with 12v input. if I increase the frequency, I can get over 1kv output.

But I have no current. none at all. if I try to power a high-speed diode (from a VCR smps) and a filter cap, it kills almost all the output. slowly charges the cap, just like a camera flash. I just cant obtain the current that I might need, then again, I may not need hardly any current at all.



Any ideas?
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Old 4th January 2006, 11:12 PM   #4
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Thats the tubes I got. an EM84. I got 5 of them, to make a spectrum. Got them really cheap too from ukraine.
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Old 4th January 2006, 11:33 PM   #5
anatech is offline anatech  Canada
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Hi mbates14,
It looks like each tube will draw around 1.6 mA closed. This is at 250 VDC.

-Chris
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Old 5th January 2006, 09:39 AM   #6
SHiFTY is offline SHiFTY  New Zealand
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You can simply use a couple of transformers back to back-

i.e. T1: 110V->12V and T2: 110V->6V.

Connect T1 to mains, connect the 12V output to the 6V winding of T2 and you will get 220VAC from the other side of T2. With a diode bridge that would be 1.414 times higher- around 310VDC, so maybe calculate a better fit.

Use decent quality transformers and rectify to a CRC filter to get required voltages. As a bonus you could use the 12V to also power two tube filaments in series.
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Old 5th January 2006, 10:35 AM   #7
nickds1 is offline nickds1  England
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Quote:
Originally posted by mbates14
I already got the tubes. And the parts to make an SMPS.
Ok, exactly how much current do I need to run a couple of these magic eyes?
I made a simple SMPS using a 555 timer, an NPN transistor, emitter resistor to burn off the current, and a filiment transformer.
I got 250 to 300 VAC output on the transformer with 12v input. if I increase the frequency, I can get over 1kv output.

But I have no current. none at all. if I try to power a high-speed diode (from a VCR smps) and a filter cap, it kills almost all the output. slowly charges the cap, just like a camera flash. I just cant obtain the current that I might need, then again, I may not need hardly any current at all.

Any ideas?
Yup - Do the sums. A 555-based SMPS will typically only be 50% or less efficient. To get 250VDC @ 8mA (5x1.6mA) you have 2W output, so you need 3W input at least. With 12VDC input, you need about 200mA+ on the input side. Your peak current will be much higher, in the region on 1A or more. The output cap MUST be very low ESR else you will never maintain the DC level - a cheap way of doing this is to use several 1uF or 2u2 300V caps in parallel. The diode must be a fast recovery type and the inductor must not saturate.

If you really want to do an SMPS, I can recommend the NEONIXIE-L forum on Yahoo!!!! The files section there has many good designs for SMPSs using 555s and more exotic specialist chips like the MAX1771 - my favourite.

I have a page on a high efficiency MAX1771-based design -
NMdS MAX1771 design - this will give up to 50mA @ 250VDC with close to 90% efficiency. Its a popular design, but be aware - SMPSs are non-trivial to get right - they are all affected by stray capacitance etc. and layout and component choice are critical. The above web page has a lot of information about this.

All in all, for valve use, back-to-back trafos may be easier!

Nick
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Old 5th January 2006, 06:38 PM   #8
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I use my diode from an old VCR smps.


The VCR smps has a Viper50 controller, but i dont think its suitable for useage in a 12v system.

Anyway, I was able, after rectification, and a 100uf at 200v cap. maintain 110vdc with the smps.


if i hook a small tube radio (4 tube type, battery powered) up to the supply, it will sag down to 24 volts. so yea, may need a better design.
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Old 5th January 2006, 06:40 PM   #9
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one slight problem. I dont have membership access to that forum.
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Old 5th January 2006, 07:18 PM   #10
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Ive been readin around google a bit.

Basically, I need a 12v to 250v "Boost Converter SMPS"

but most of them use those specialty chips that I dont have.


so i would have to keep it at a transistor level, or use a 555.


Any ideas?
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