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Vacuum Fluorescent Display Amplifiers For Primitive Radio

from H. P. Friedrichs, AC7ZL on December 10, 2008
Website: http://www.hpfriedrichs.com/
View comments about this article!

Vacuum Fluorescent Display Amplifiers For Primitive Radio

By, H. P. Friedrichs, AC7ZL
http://www.hpfriedrichs.com/


Introduction

Vacuum tubes represent an electronic technology whose roots extend a century and more into the past. With the exception of their continued use in certain niche applications, they have all but vanished from contemporary electronics, having been replaced by an endless array of solid state switching, amplification, and display technologies. Yet, despite all of this, it seems that interest in vacuum tubes and the "hollow state" technology that makes them work refuses to die.

A Typical Vacuum Tube

Iíve done a fair bit of tinkering with vacuum tubes, even to the extent of building a few of my own. I actually wrote a book about it. This article, however, comes from a different vantage point. In essence, Iíve identified a piece of contemporary electronic junk that, while not intended to be a vacuum tube in the classic sense, shares the necessary features of radio tubes. It can be induced to amplify feeble audio signals from primitive radio gear like crystal radio sets. Such experimentation is a lot of fun, and the end result is actually useful.

That said, let us not overlook the fact that most vacuum tube experiments, including the ones to follow, involve the use of high voltages. Besides the obvious dangers associated with electric shock, miswired batteries can overheat and short circuits can produce fire. My presumption is that the reader is familiar with basic electrical principles, competent with regard to safe practices, and endowed with some level of common sense. Remember, you are responsible for your own safety.

Basic Tubes

Before I describe what Iíve been playing with, it is worthwhile to engage in a quick review of what makes a classic vacuum tube what it is. It would actually take volumes to discuss this in a comprehensive manner, but letís summarize things this way. We start with a common light bulb, that is, a wire filament contained in a glass bulb from which all the air has been evacuated. If we add a metallic plate to the interior of the bulb, and place a positive charge on that plate, electrons will actually leave the surface of the heated filament, float through the space between the filament and plate, and strike the plate. In other words, an electric current can be made to flow between the filament and plate. Current will not flow from the plate back to the filament, making such an instrument a one-way check-valve, or diode.

The diode form of tube has numerous applications, not the least of which is the extraction of audio from amplitude modulated (A.M.) signals. But letís put that aside for the moment.

Once we set things up in the tube described above, the current between the filament and plate is constant. However, if we introduce a wire mesh or "grid" between the filament and the plate, and then apply varying electrical charges to that grid, we find that the flow of current between the filament and plate will also vary. This is the essence of amplificationóthe idea that a tiny signal can be used to control the flow of a more powerful energy source.

The triode (From Vacuum Tubes in Wireless Communication, Bucher, 1919)

.

The Vacuum Fluorescent Display

Many of the electronic gadgets in the modern world speak to us through information displays of some kind. All sorts of display technologies are used to communicate functional status and numeric values like time, voltage, temperature, weight, and mileage. Among these is the vacuum fluorescent display, or VFD.

VFDs are luminescent displays, that is, they glow. VFDs typically emit a pleasing blue-green light, and the glowing images produced by the VFD can be fashioned to represent numbers, letters, bar graphs, icons, or other symbols. Where can one find VFDs? Everywhere! They are commonly used as displays in appliances like microwave ovens. They are used in industrial electronics like digital panel meters and thermometers. Iíve seen them in toys, bathroom scales, stereo equipment, and office phones. The information display for the entertainment system in my 2008 Ford is a VFD.

Internal Structure of the VFD

Like a vacuum tube, a typical VFD consists of a glass container from which all the air has been removed. Because VFDs are display devices, the glass envelope tends to be somewhat flat and rectangular in shape. The display characters-- the symbols, words, and segments that actually light up-- are composed of electrodes called anodes that are coated with phosphorescent chemicals. Typically, these chemicals contain zinc, selenium, sulfur, and other trace materials.

Stretched across the interior of the container, suspended above the display characters, are several filament wires. These wires are powered by a low-voltage supply to heat them. Although these filaments lie between the observer and the characters, they are composed of exceedingly thin wire and are not heated to more than a very dull red, so you wouldnít even notice them unless you actually looked for them.

If we apply a source of low voltage to the filament, it will heat up and generate a cloud of electrons. If we then apply a high-voltage positive charge to the characterís electrodes (the anodes), electrons produced by the filament will be attracted to this positive charge, and will strike the phosphorous chemical coating on the characters. When stimulated in this fashion, the characters glow.

Of course, when the display is in use, we donít want all of the display items to be glowing at once. Rather, we want to be able to control the display features independently, and turn them on and off as necessary. To enable this, VFDs contain another structure: a thin mesh or grid that lies between the filament and each phosphorescent display feature. If we apply a positive charge to the grid, electrons from the filament are encouraged to move toward the phosphors and induce them to light. If a negative charge is applied to the grid, electrons from the filament are repelled, they fail to reach the phosphors, so the display feature goes dark.

Below is a photomicrograph of a section of a typical display. In this image one can see a display feature/anode (the word "TEST"), a honeycomb-like control grid that covers the word, and one of the displayís five filaments, which appears as a thin, white, horizontal line suspended above the grid.

Internal features of the VFD

While the purpose of a VFD is very different than that of the average radio tube, there are similar structures in both. Both contain an electron source, the filament. Both contain a positively charged target. In the radio tube, this electrode is called a "plate." In the VFD, this electrode is called an "anode," and takes the form of a phosphor-coated word, symbol, or display segment Finally, each device contains a grid structure, which is used to control the flow of electrons from the filament to the anode/plate. The similarity between VFDs and the types of radio tubes Iíve been used to playing with prompted me to wonder if a VFD could be used as an amplifier. Interestingly, the answer is a definite yes.

Wiring Up a VFD

Wiring up a VFD is a simple matter. The key is knowing which terminals on the VFD do what. This information can be arrived at in two ways. If one is lucky, a Google search of the part number for a display may yield a manufacturerís datasheet. A datasheet will indicate which pins are connected to which internal structures, and it will also provide useful information regarding the proper voltage to apply to the filament. The other way to derive hookup information is to study the display visually, make a few measurements with an ohmmeter, and deduce what one needs to know from these observations. My VFDís were salvaged from junk, so I took the latter route.

The first step is to identify the filament terminals. The filaments appear as long, thin, hair-like wires that run parallel to the long axis of the display. I would expect to find at least three, or possibly more, but the exact number depends upon the type and dimensions of the display. The ends of each filament wire terminate at little metal bars or tabs. The tabs feed electricity to the filaments, support them, and in some cases, maintain tension on them so that they wonít sag. The first goal, then, is to study the VFD and its internal structures to determine which pins are connected to the filament.

The VFDís internal structures are connected to external pins through strips of thin metal or conductive traces that are applied to the glass inside of the VFD. Knowing this, one can simply follow the path of these traces with the naked eye.

Traces on the backside of the VFD

Once a pair of filament terminals have been identified, they can be verified with a multimeter set to read ohms. If one probes between suspected terminal pins, one can expect to see conductivity and a resistance reading one the order of 10ís of ohms.

Next, one must identify the pins associated with each character or display feature, the VFDís anodes. This is purely a matter of visual inspection. One chooses a display feature-- a word, symbol or perhaps a segment of a numeric figure-- and then tries to identify a signal path from that feature back to one of the external pins. This determination must be done for all of the display features. As my VFD was a reasonably complex device, I recorded which feature/anode connected to which pin on a sheet of lined paper.

Finally, all of the grid connections must be identified. This is also a visual exercise. One must choose a grid, study the VFDís internal construction, and identify a path from that grid to one of the external pins. This must be repeated for each of the grids in the VFD. Again, I found it helpful to record my findings on paper as I studied the device.

Lighting Up the VFD

Lighting up the VFD requires two power supplies, a low-voltage supply for the filament, and a high-voltage anode supply to light up the characters.

Filament power requirements differ depending upon the specific VFD. However, of the parts Iíve tinkered with, the lowest filament voltage I saw was on the order of 3 volts, and the highest appeared to be 6 volts. I would suspect that other VFDís have requirements that will fall in this range.

Filament voltages are easily achievable with flashlight batteries. Two "D" cells wired in series will get you 3 volts. For a 6-volt filament, 4 "D" cells in series are the answer. Batteries work just fine, but I preferred to take advantage of one of the variable power supplies on my bench. In any event, the supply is connected to the filament terminals that were identified earlier. When all is well, the filaments should barely glow when viewed in a darkened room. If the filaments are bright red, this is indicative of filament voltage that is far too high. Continued operation at this level will eventually burn out the display.

VFDís also require a high-voltage supply to light the display features. In normal use, the "high-voltage" supply can actually be quite low, i.e., I have lit VFDs with as little as 15 volts on their anodes. However, in the radio application I am about to describe, higher voltages work much better. In that case, a D.C. power supply on the order of 90 volts or greater is just the ticket.

As is the case with filament voltages, the high-voltage anode current can be supplied with batteries. Ten 9-volt batteries, connected in series, will deliver 90 volts. Given the modest energy requirements of the VFD, batteries are a practical power source, and ten batteries in series should last a long, long time.

A comment is in order, here. A 90-volt battery is capable of inflicting an unpleasant shock. There is also sufficient energy in such a battery to cause a fire if it is abused. I have built high-voltage batteries of this type myself. I always prefer to install them in an insulated container, which is then fitted with binding posts or fahnestock clips. I usually insert a small fuse inside the battery container, wired in series with the batteries, to safely limit the current in case Murphy strikes and a mistake is made. In this particular instance, I avoided having to build a high-voltage battery by using a variable power supply I constructed a few years ago.

To light up the VFD, we first activate the filament as described above. The negative terminal of the high-voltage supply is connected to one of the filament terminals (it doesnít really matter which) and the positive terminal of the supply is connected to one of the VFD pins that feeds a character or symbol anode. Finally, the grid (corresponding to the feature we desire to light), is connected to the positive side of the high voltage supply through a large resistorósomething on the order of 4.7 megohm. If the VFD is wired in this fashion, the experimenter will be rewarded with blue-green light. If one applies the appropriate signals to other grid and anode pins, other display features can be made to light.

A circuit to light up the VFD

For the purpose of the experiments to follow, the final preparatory step is to use a soldering iron and some wire to connect all of the anodes together. Likewise, we must connect all of the grids together. This leaves a VFD with what amounts to four terminals: two filament terminals, one "super" grid terminal (the sum of all grids), and one "super" anode terminal (the sum of all anodes). In this "super" configuration, a positive high voltage applied to the "super" anode (with the 4.7 megohm resistor connected to the "super" grid) should light up all of the display features simultaneously.

The VFD Amplifier

One of the first observations I made occurred after I had lit my VFD in the "super" configuration. I broke the anode connection and inserted a high-impedance headphone into the circuit. I lifted the grid terminal and allowed it to "float." Immediately, the headphone was filled with a deep 60-cycle buzzóthe kind one hears if the patch cord for a guitar amplifier is left dangling. It was obvious that the VFD was functioning as an audio amplifier. This prompted me to wonder if there was benefit in connecting this to a crystal radio.

The CDROM radio

Amplifying the output of the CDROM radio. From left to right: Headphones, high-voltage power supply, low voltage supply, CDROM radio, and in the center, two different VFDs.

Simplified schematic for the CDROM radio and VFD amplifier. Click here to see it in higher resolution.

Above is an image of my "CDROM" radio, a crystal radio set based upon the container in which CDROMs are sold. I connected this radio to the VFD as represented in the simplified schematic above. Music came blasting through the headphones. Despite the fact that my antenna consisted of no more than 15 feet of wire thumb-tacked to the ceiling, the amplifier worked so well that the volume in the headphones was unpleasantly loud. During this period of experimentation, I made note of the following details:

a) The amplifier works when the audio signal from the crystal set is positive with respect to ground. It is almost completely non-functional when the detector diode is reversed and the audio signal becomes negative with respect to ground.

b) The VFD can function as both detector and amplifier. I verified this by bypassing the diode in the CDROM radio. Volume was reduced, but the amplifier still worked just fine.

c) The apparent gain of the amplifier is dependent upon the voltage applied to the "super" anode of the display. I have a variable high-voltage power supply. The amplifier provided useful amplification with an anode voltage of about 60 volts. At 90 volts, the amplifier worked much better. At 150 volts, the audio in headphones was so loud that music and speech could be heard with the headphones simply lying on the table.

d) Anode current never exceeded 6 milliamps. While this limits the VFDís usefulness as a general purpose amplifier, it is more than up to the task of driving high impedance headphones.

e) A voltage gradient, apparently caused by the voltage drop along the filaments, causes a column of character blocks to assume an interesting triangular shape.

f) Strong local stations cause the display to modulate, i.e., become brighter and darker as the audio varies. This is not only interesting to watch, it is potentially useful as a tuning indicator.

Image of operating display showing voltage gradient across the width of the display

g) A magnet applied to the face of the VFD causes visible distortions in the display and appears to have some affect on the gain of the tube, depending upon the magnetís strength and orientation.

h) The planar construction of the tube makes it susceptible to nearby electrical noise. Noise in the audio channel can be greatly reduced by placing the VFD inside of a grounded metal box, or by laying a grounded metal plate upon the face of the display.

i) At one point, I replaced the headphones in the circuit with a small transformer, and used this to feed audio into my desktop computer to make a recording.

Audio transformer used to make recordings

Image of characterization setup

Characterization Schematic (From Vacuum Tubes in Wireless Communication, Bucher, 1919)

The great success of the VFD as an amplifying device prompted me to try to collect data to characterize it. To do so, I used variable power supplies to apply a series of voltages to the "super" anode and to the "super" grid. This, I did while simultaneously monitoring the anode current. This data was collected in a spreadsheet and then graphed using Excel.

Plate current as a function of plate voltage. Click here to see it in higher resolution.

Plate current as a function of grid voltage. Click here to see it in higher resolution.

Tube characterization data. Click here to see it in higher resolution.

Conclusion

On this basis of this data, it appears that the particular VFD I was playing with, depending upon operating point, offers amplification on the order of 15 to 20 timesóa respectable amount of gain.

While the triode vacuum tube and VFDs share comment internal features, it doesnít appear that VFDs can be wired to take advantage of grid-leak bias. And, despite the significant gain apparent in the VFD, I was not able to get it to function in a regenerative circuit. This shortcoming, however, might possibly be overcome with alternative biasing methods.

Samples of A.M. radio recorded with this equipment can be heard by clicking the following hyperlinks: smilesmilesmile instrumental

I have also prepared a short video, showing the VFD amplifier in operation, which can be found on Youtube here.

(This article was originally prepared for, and appeared in, the newsletter of the Xtal Set Society. Check them out!)

73 Pete
AC7ZL

Member Comments:
This article has expired. No more comments may be added.
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by AC5UP on December 10, 2008 Mail this to a friend!
Absolutely outstanding article!

Not only is this weird science at its finest, but a superior example of thinking outside the box... I have no doubt we'll be seeing an adaptation by the toob audio crowd taking them past the Blue LED stage of product differentiation and marketing.

Well Done, OM.
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by AC0GR on December 10, 2008 Mail this to a friend!
Have you done any frequency sweeps to determine the full bandwidth? Perhaps possibilities as a VLF/ELF front end stage?

 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by KB2DHG on December 10, 2008 Mail this to a friend!
FANTASTIC AND INTERESTING ARTICLE!
WOW I AM SO JELIOUS... I wish I had time on my hands to play and experament... This article has sparked my interest to learn more (no pun intended)
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by K0BG on December 10, 2008 Mail this to a friend!
Some people have WAAAAAY to much time on their hands!

I too would like to know just how high up in the spectrum the "amp" has gain.

Alan, KōBG
www.k0bg.com
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by N3OX on December 10, 2008 Mail this to a friend!
"Some people have WAAAAAY to much time on their hands! "

And yet, they contribute the best eHam articles ;-)

This is awesome! I actually saw another one of these the other day on Make: Blog used as a headphone amp... there was some discussion of this article there too in the comments.

Clever and fun, and I appreciate the REAL DATA.

And needless to say, much better than someone tossing off a rant about some aspect of electromagnetism they don't understand.

I suspect the VFD-as-audio-amplifier is going to be the next big geek-project on the internet. The Nixie tube clocks and so forth really got people excited for a while, and vacuum fluorescent displays are much easier to come by.

Well done.

73
Dan
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by AC7ZL on December 10, 2008 Mail this to a friend!
Thank you, all, for the kind remarks.

I would add that some of the hyperlinks in this copy of the article don't seem to be working. If you visit my website, you can see the original article where all the links work.

For example, I have two short MP3 clips that allow you to hear the circuit in operation. these can be found in the original article on my site.

As well, there is a "live" demonstration of the circuit on Youtube. You can find that video, either by clicking on the hyperlink in the article on my web page, or you can go to Youtube, and in the search box, type AC7ZL.

Finally, I have received inquiries with regard to the CDROM crystal radio. Plans for that appear on my web site, and I invite everyone to stop by and take a look around.

73,
Pete
AC7ZL
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by N2KFC on December 10, 2008 Mail this to a friend!
Hello,

Very nice Article,brings some nostalgia abt Vacuum Tubes...In the past,I did a lot of Projects with Vacuum Tubes,last one in 1972/73 was a TRX with 7360 at RX input...

73!
John,SP2GGZ, N2KFC, YB1AQV,
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by W5PJW on December 10, 2008 Mail this to a friend!
Excellent article! Lots of "meat" here. Data, graphs, schematics, pictures, well written and interesting! I love it!

73, Mark
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by N0YXB on December 10, 2008 Mail this to a friend!
Thanks for a great article Pete! And great remarks by N3OX (Dan), I couldn't have said it better. Don't let the ranters get you down. Hope to see more articles like this.

Vince
N0YXB
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by KG6WLS on December 10, 2008 Mail this to a friend!
Neat!! This is the kind of read that most of us like to see. Perhaps THIS article will be an "eHam Classic" someday.

Thanks for the effort!

73 KG6WLS
Mike
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by W4VR on December 10, 2008 Mail this to a friend!
I think you should submit your article to QST and see what happens. W4VR
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by WI7B on December 10, 2008 Mail this to a friend!
Great article. Tinker on!

73,

---* Ken
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by KQ6EA on December 10, 2008 Mail this to a friend!
Best thing I've seen on eHam in the last couple of years....
Well done, sir!
73, Jim
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by KC0RBX on December 10, 2008 Mail this to a friend!
WOW!!! Now these are the kind of articles I like to see on EHAM!! Great article, great content and good writing.
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by KE3WD on December 10, 2008 Mail this to a friend!
Now THIS is hamming!


Outstanding, sir.


KE3WD
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by AD7WN on December 10, 2008 Mail this to a friend!
Pete, you need to get out more :-) That having been said, this is a very well written article. Well done.

73 de John
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by K9CTB on December 10, 2008 Mail this to a friend!
This is the sort of article that brings great credit to amateur radio. Thanks very much! I'll make the no-brainer prediction that this will be among those "eham classic" articles.

73 de Neil
K9CTB
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by NV5E on December 10, 2008 Mail this to a friend!
Outstanding indeed! Articles like this are one of the reasons I enjoy amateur radio so much.
Rob
NV5E
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by KC3L on December 10, 2008 Mail this to a friend!
Fantastic article!

Lee
KC3L
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by KM3F on December 11, 2008 Mail this to a friend!
Well written but would add in the early part that the electrons released by the filiment are negitively charged and are attracted to the positive plate element by the electric field lines of force in the space between the elements and not just float from one element to the other.
All vacuum tubes will be influened a magnetic field in the imediate vacinity as indicated by how a CRT functions by sweeping the screen moving the electron beam with either an applied electric field to internal plates or a magnetic field applied by a coil winding external to the beam.
A tube's ability to 'oscillate' is dependent on it's gain, the tuned elements in the external circuit, feed back and the distance between the elements affecting electron transit time.
For example a miniture triode can be made to oscillate with small parrallel line attached directly to it's plate and grid pins at frequencies as high as 1200 Mhz where the limit is transit time between the kathode and the plate independent of plate voltage.
Good helping of tech for modern hams.
Worked in the industry for some years building small RF apmlifier tubes, transmitter tubes, nixie tubes, noise sources, Klystrons at 75 Ghz and traveling wave tubes.
Brings back old memories.
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by N4CQR on December 11, 2008 Mail this to a friend!
Excellent and entertaining article. Thourghly ennjoyed it.

BTW, we have a few members that suffer from delusions of grandeur. Accept it for that and move on.

C r a i g

 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by WR8Y on December 11, 2008 Mail this to a friend!
What we have here is an instant eHam classic.
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by EC158 on December 11, 2008 Mail this to a friend!
KB2DHG

Don't be "jelious". If you do get any extra time, don't waste it on "experaments", spend it on learning how to spell.

 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by N0YXB on December 11, 2008 Mail this to a friend!
EC158, don't be so pompous. At least he has his ham ticket. Maybe you should go back to "shooting skip on CB" with your "Cobra 142 GTL, Euro Expander 500 Mic, D&A Phantom Linear Amplifier, Moonraker IV Antenna" as listed in your profile.

Vince
N0YXB
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by EC158 on December 11, 2008 Mail this to a friend!
N0YXB

I'm so flattered that you read my profile! Yes I do have quite the setup for shooting skip, but I don't like to brag. MY HAM setup isn't quite so elaborate, but it works well too.

Thanks Vince, 73's and 88's
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by W0FM on December 11, 2008 Mail this to a friend!
Absolutely had me glued to the screen, Pete. Very nice piece of writing, while also regenerating memories of electronic experiments I conducted in my youth. Not hardly on your level, unfortunately.

Thanks for a great submission.

73,

Terry, WōFM
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by KF7CG on December 11, 2008 Mail this to a friend!
Sounds like your VFD is similar to the old "zero bias" power tubes for class B operation. There is no anode current without forward bias. With a small control grid structure and low anode current it will always be hard to generate "gred leak" bias. The VFD would probably like to have a small positive bias on the grid as opposed to the negative bias used by most tubes.

Thanks for a great article. I would never have though of a VFD as a tube.

KF7CG
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by KB1GMX on December 11, 2008 Mail this to a friend!
Interesting that there is still interest in this.

Many years ago I played with similar VFDs. However I had some that were one digit per bottle (T13/4 size) that I'd had gotten around 1975. I tried them as a triode in a radio for laughs and it worked well. I did some measurements and found the depending one what side of the heater was ground I could use the heater battery (1.5V)as "bias". I also measured the mu of the "tube" and found they were in the range of directly heated low mu triodes. As a result I tried one in a regen RX and found it worked well with 36V (4 pieces 9v battery). It's still in the junk box as a "plank radio" and it did work as well as a typical 3A5 or similar directly
heated battery tube.

I haven't tried the multi-element VFDs but the larger heater and it's greater voltage would have more effect on grid bias due to voltage drop along the length of the VFD. It helps explain the brighter at one end effect.

They seem to work to low HF fairly well though I only tried it to 75M.

Allison

 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by WA3YAY on December 11, 2008 Mail this to a friend!
Good job. I only understand about half of this article, but good job anyway!
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by VE7RWN on December 11, 2008 Mail this to a friend!
Thank you Pete, for an excelent article. I look forward to reading more about your experiments on this project, and how versatile this application could become for our hobby.
Terry, W0FM, your old ft847 is still working nicely for me. Thanks!

Tnx and 73
Rob, VE7RWN
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by N3KBS on December 12, 2008 Mail this to a friend!
I just want to say - Really Cool!
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by NA0AA on December 13, 2008 Mail this to a friend!
I don't understand half of this, but it's always great to see something used in an unexpected way - and work.

My next thought is that with enough segments could you run it as a multiple part amplifier?

Great stuff.
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by KF7CG on December 16, 2008 Mail this to a friend!
Since the only structure common between the different display elements is the filament, have you tried grouping the anodes and grids to form two "tubes" with a common cathode? This configuration could lead to push-pull amplifier and "Darlington" type circuits.

Here is an idea. You could separate various sections of the VFD and drive each different section with a tuned circuit giving you an indicating spectrum sniffer.

KF7CG
 
Vacuum Fluorescent Display Amplifiers For Primitiv  
by K8CKW on December 19, 2008 Mail this to a friend!
Wow! It's great to see an amateur doing hands on creation of components long thought beyond the means of mere mortals! And the documentation, pictures, and entire web site is pleasure to read and visit. Hats off to you sir for a great and infomative job.

 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by BHARDIMON on December 29, 2008 Mail this to a friend!
Are hams involved in anything that's not 40 years behind the times ? Embarrassing.
 
RE: Vacuum Fluorescent Display Amplifiers For Prim  
by W8JII on December 29, 2008 Mail this to a friend!
"Are hams involved in anything that's not 40 years behind the times ? Embarrassing."

The only thing that's embarrassing is your ridiculous comment..This is an excellent article.
 
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