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Old 9th Jun 2006, 7:38 pm   #1
adibrook
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Default the VFD amp!!!

In my everlasting quest for wierder technology, i stumbled on somethign interasting.

VFD's (vaccum flourescent displays), such as the ones used in DVD players VCR's and stereos, are actually triodes!

I allways though they were cold-cathode devices kind of like nixie tubes, but with each anode coated in a phosphor. But it turns out they arnt.

-They have directly heated oxide cathodes.
-They have grids

I didnt know that untill a few months back when i read somethgin about them.

Turns out they are like a glorified magic eye tube.

There are 7 grids, and each little segment is a phosphored anode.

So, i built a prototype audio amp using one of these! I';ll get some pics of it later today.

It uses a pot to control anode voltage, the ''sweet spot'' being at approx 150v ish. And i used a 100K pot to give it heater voltage from a 6.3VDC supply. I keep it at minimum working heater voltage (if you turn it up past 1.5v it makes no difference anyway). Hopefully the heater wont blow too soon.

It works!!!!

I used an L63 for drive and connected all the anodes and grids of the VFD in paralell.

I used 1K and 100uf on the cathode and 1M on the grid, as with any small valve.

The VFD is powering an audio transformer direclty. It aint loud, but the sound quality sounds good.

Pics coming.

hehehhe...this is crazy. I'm not aware of this being done before, but it probably has. Either way i thought of it independantly.

I never actually expectid it to work. I guess that just proves that anythgin with a grid can amplify sound.
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Old 9th Jun 2006, 7:55 pm   #2
Jim - G4MEZ
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Default Re: the VFD amp!!!

Excellent stuff Adi, well done Can't wait to see the pictures!

I am well impressed. Can you make the display show "ECC83" whilst it is working just to really put the icing on the cake
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Old 9th Jun 2006, 8:28 pm   #3
adibrook
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Default Re: the VFD amp!!!

Ok.

Hers the 1st prototype. Assembled on a piece of wood with nails as terminals.

http://img.photobucket.com/albums/v4...ok/dispamp.jpg

Unfortunatly if i make it say ECC83 than only a few of the anodes will eb used, which woudl decrease it's power handling capability. I'm using all avalible anodes for mazimum current at the moment.

However, if in the next prototype i want to see how well it works as a preamp. Then i wouldnt need high current, so i could make it say ecc83. That woudl be cool.

The prototype is all valve expet form a ''dirty silicone'' bridge rectifier to provide DC for the VFD heater.
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Old 14th Jun 2006, 11:49 am   #4
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Default Re: the VFD amp!!!

Are they actually designed to run at "normal" valve voltages too then, or have you just gotten lucky? I've not heard of 100V supplies in DVD players thats all! I'd quite like to use one as an actual display, rather than an amplifier stage.
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Old 14th Jun 2006, 1:37 pm   #5
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Default Re: the VFD amp!!!

I think theyre only really supposed to run at about 14v. Thats what i read in a tutorial anyway. But i'm running this one on the best voltage it amplifies on, which is somewhere between 0 and 250v.

It isnt showing any signs of distress yet. So i presume it's coping. But hey...if it dies it dies. I got it form a vcr that someone dumped outside my back door. (all donations welcomed ).
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Old 14th Jun 2006, 3:45 pm   #6
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Default Re: the VFD amp!!!

Hi Aidy

You're a legend

I briefly looked at that type of display for a commercial project, (Id have never considered them, even briefly, if I had to arrange for a 150V supply) but they were awesomely expensive (relative to LCDs) at low volumes - Yet they appear in cheapo consumer goods!! Anyway, you shouldn't have any trouble with spares if the thing only lasts a while.
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Old 15th Jun 2006, 4:27 pm   #7
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Default Re: the VFD amp!!!

I remember playing with a VFD when I was about ten and I ran the filliments off of an AA cell and the HT side from 2 9v PP3's in series, it was very bright.
How bright are yours at 150v Adi? they must be fearsomely bright, I can't tell from the pictures.
Well done by the way, I admire your new ideas and getting them from design to working prototypes. Keep up the good work!

Lee
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