I can ask.
But the Professor made it clear that it (audio application) is not their field of expertise.
http://www.physics.usyd.edu.au/app/research/plasma/index.html
But the Professor made it clear that it (audio application) is not their field of expertise.
http://www.physics.usyd.edu.au/app/research/plasma/index.html
Jesper,
I would choose a material that easily emits electrons (search for the "work potential" of materials- e.g. in Fluegge, Handbook of Physics). Tungsten seems to be very good. It also is very stable with respect to temperatures. You can look what materials are used in electron tubes but there you have more choices because inside a vacuum tube there is - well, as the name says- vacuum. So no oxidation asf.
I am not sure what materials such as LaB6 will do under the conditions met in a plasma tweeter.
Tungsten certainly ain't bad and I THINK alloys of Tungsten and Silver should also work pretty fine.
Regards,
Peter
I would choose a material that easily emits electrons (search for the "work potential" of materials- e.g. in Fluegge, Handbook of Physics). Tungsten seems to be very good. It also is very stable with respect to temperatures. You can look what materials are used in electron tubes but there you have more choices because inside a vacuum tube there is - well, as the name says- vacuum. So no oxidation asf.
I am not sure what materials such as LaB6 will do under the conditions met in a plasma tweeter.
Tungsten certainly ain't bad and I THINK alloys of Tungsten and Silver should also work pretty fine.
Regards,
Peter
Hello plasma friends,
For some time I read here only because I simply lack the leisure to work and continue to improve something, I am pleased with my investment as it is very satisfied and it's still working like it here in the forum to be seen.
Now I want a new and stronger system because my friend something for his PA wants, I have to be a circuit with two tubes thought, without exhausting and with a performance at the 135 db go.
The winter is with us rather slowly past, and in my workshop it is still cold, that is really the main reason because I have nothing to work with.
But I have a new idea, and I will you imagine if it is processed.
Only tungsten again, so does the device as I now have works wonderful, little burn, at least I still have nothing to polish or replace, it is still the first choice.
I am very pleased that you thought about a lot, but ask a question, because someone has been trying the reconstructed what I have done or wasted your time only in theory?
Many greetings from the cold Odenwald, Hessen
George
For some time I read here only because I simply lack the leisure to work and continue to improve something, I am pleased with my investment as it is very satisfied and it's still working like it here in the forum to be seen.
Now I want a new and stronger system because my friend something for his PA wants, I have to be a circuit with two tubes thought, without exhausting and with a performance at the 135 db go.
The winter is with us rather slowly past, and in my workshop it is still cold, that is really the main reason because I have nothing to work with.
But I have a new idea, and I will you imagine if it is processed.
Only tungsten again, so does the device as I now have works wonderful, little burn, at least I still have nothing to polish or replace, it is still the first choice.
I am very pleased that you thought about a lot, but ask a question, because someone has been trying the reconstructed what I have done or wasted your time only in theory?
Many greetings from the cold Odenwald, Hessen
George
@3142
Is work potential the same as electronegativity (pauling scale)? Or is there another word for it? I could not really find work potential information via google and the book you mention is not available through my normal sources (library)?
Spring is coming where I live (Denmark) Birds singing, more sun, warmer. I really like it
Regards,
Jesper
Is work potential the same as electronegativity (pauling scale)? Or is there another word for it? I could not really find work potential information via google and the book you mention is not available through my normal sources (library)?
Spring is coming where I live (Denmark) Birds singing, more sun, warmer. I really like it
Regards,
Jesper
Mea culpa, Mea maxima culpa. I apologize
I had a wrong translation of the german term AUSTRITTSARBEIT. Correct translation seems to be WORK FUNCTION.
Look at WIKIPEDIA. There is a list of work functions for different materials (at least on the german wiki) There is also ON THAT SAME PAGE a link to a document relating to plasma.
That should help
Regards
Peter
I had a wrong translation of the german term AUSTRITTSARBEIT. Correct translation seems to be WORK FUNCTION.
Look at WIKIPEDIA. There is a list of work functions for different materials (at least on the german wiki) There is also ON THAT SAME PAGE a link to a document relating to plasma.
That should help
Regards
Peter
No worries
Well, yes, languages may have it's challenges. Yesterday I looked at a movie of a French radio amateur who was building his own vacuum tubes. I found the video in itself to be very interesting and also happened to go to his website. I speak a reasonable French but out of curiosity decided to try a French - English translation through Google. To me that rendered the text not very legible - not easily understood. It surprised me since I guess that Google probably has a quite good translation software.
Anyway - I found "work function" in wikipedia - very helpful - thanks for the tip!
Regards,
Jesper
Well, yes, languages may have it's challenges. Yesterday I looked at a movie of a French radio amateur who was building his own vacuum tubes. I found the video in itself to be very interesting and also happened to go to his website. I speak a reasonable French but out of curiosity decided to try a French - English translation through Google. To me that rendered the text not very legible - not easily understood. It surprised me since I guess that Google probably has a quite good translation software.
Anyway - I found "work function" in wikipedia - very helpful - thanks for the tip!
Regards,
Jesper
@ George Green
I find your design, experiences, and choice of materials very interesting. Although I will not build a plasma tweeter, yours, and other's, input in this thread has been very helpful (I'm interested in something inspired by a plasma microphone although I hope the practical implementation will not involve the plasma state as I find it less convenient for a microphone).
Smile to your day....
Jesper
I find your design, experiences, and choice of materials very interesting. Although I will not build a plasma tweeter, yours, and other's, input in this thread has been very helpful (I'm interested in something inspired by a plasma microphone although I hope the practical implementation will not involve the plasma state as I find it less convenient for a microphone).
Smile to your day....
Jesper
This may arrive too late to be of use, and glosses over some details in the interest of focusing on the key features, but I'll toss it in just in case it's helpful to someone.
Electronegativity refers to the tendency for an atom to draw electron density toward itself when it participates in a chemical bond. Elements with high electonegativity (fluorine, oxygen) strongly draw electron density toward themselves and tend to polarize bonds they participate in. Electronegativity has no units.
Work function refers to the minimum amount of energy capable of removing an electron from a particular material. Materials with higher work function require more energy for electron removal. It's measured in energy units (joules, eV, etc.).
Few
Electronegativity refers to the tendency for an atom to draw electron density toward itself when it participates in a chemical bond. Elements with high electonegativity (fluorine, oxygen) strongly draw electron density toward themselves and tend to polarize bonds they participate in. Electronegativity has no units.
Work function refers to the minimum amount of energy capable of removing an electron from a particular material. Materials with higher work function require more energy for electron removal. It's measured in energy units (joules, eV, etc.).
Few
@ few
Thanks for the clarification. Could it be then, that a theoretically ideal material for a plasma state transducer would be a material with a low electronegativity and also a low work function?
Or maybe a low electronegativity for the cathode and a high electronegativity for the anode?
Provided that the material can manage the heat as well?
Jesper
Thanks for the clarification. Could it be then, that a theoretically ideal material for a plasma state transducer would be a material with a low electronegativity and also a low work function?
Or maybe a low electronegativity for the cathode and a high electronegativity for the anode?
Provided that the material can manage the heat as well?
Jesper
@ George Green
Hi George,
I was thinking - in order to free electrons to be used in the plasma, have you tried to place a coil - sort of what is done in indirectly heated vacuum tubes - around your iron & tungsten cathode?
Either modulated at a low voltage with the plasma tweeter signal or fully disconnected from the rest of the circuitry so that it only provides electrons.
It might be a (easy) way of freeing electrons for the plasma signal - sort of like an electron pool ...
Jesper
Hi George,
I was thinking - in order to free electrons to be used in the plasma, have you tried to place a coil - sort of what is done in indirectly heated vacuum tubes - around your iron & tungsten cathode?
Either modulated at a low voltage with the plasma tweeter signal or fully disconnected from the rest of the circuitry so that it only provides electrons.
It might be a (easy) way of freeing electrons for the plasma signal - sort of like an electron pool ...
Jesper
Jesper,
in a plasma transducer you first have to produce a plasma. You do so by using electrodes that emit electrons. The more the better, obviously. Electrodes are solid state (unless you want to melt them....). Electron emission from solid state body is governed by work functions. That is what you have to look at. FULL STOP.
As FEW said, electronegativity governs the behaviour of ATOMS in MOLECULES (and a physicist means molecules spaced far apart---thus NOT solid state where you got a bunch of atoms close together). So you would have to look at the plasma itself.
However, you would not want to mess with the plasma molecules surrounding the electrode because changing them would mean that you had to have some sort of gas supply for e.g. making the gas FLUORINE (even worse than Ozone regarding toxicity, but electronegativity of 4!). Even if you WERE to change the gas from AIR to say Helium you d be looking for properties other than electronegativity. So: just forget about ELECTRONEGATIVITY completely.
Regards
Peter
in a plasma transducer you first have to produce a plasma. You do so by using electrodes that emit electrons. The more the better, obviously. Electrodes are solid state (unless you want to melt them....). Electron emission from solid state body is governed by work functions. That is what you have to look at. FULL STOP.
As FEW said, electronegativity governs the behaviour of ATOMS in MOLECULES (and a physicist means molecules spaced far apart---thus NOT solid state where you got a bunch of atoms close together). So you would have to look at the plasma itself.
However, you would not want to mess with the plasma molecules surrounding the electrode because changing them would mean that you had to have some sort of gas supply for e.g. making the gas FLUORINE (even worse than Ozone regarding toxicity, but electronegativity of 4!). Even if you WERE to change the gas from AIR to say Helium you d be looking for properties other than electronegativity. So: just forget about ELECTRONEGATIVITY completely.
Regards
Peter
Good to know ... So, I'll leave the electronegativity to itself.
However regarding electrons surrounding an electrode it is mentioned in Linsley Hood's "Valve & transistor Audio Amplifiers" that the electron pool surrounding the cathode in a vacuum tube reduces e.g. flicker noise. I do not know if it would be the same in free air, though.
Jesper
However regarding electrons surrounding an electrode it is mentioned in Linsley Hood's "Valve & transistor Audio Amplifiers" that the electron pool surrounding the cathode in a vacuum tube reduces e.g. flicker noise. I do not know if it would be the same in free air, though.
Jesper
Dukane Ionovac two-way for sale!
http://cgi.ebay.com.au/EXTRA-Rare-D...NameZWD2VQQcmdZViewItemQQ_trksidZp1638Q2em122
worth a look just for the pictures.
http://cgi.ebay.com.au/EXTRA-Rare-D...NameZWD2VQQcmdZViewItemQQ_trksidZp1638Q2em122
worth a look just for the pictures.
Tuning plasma tweeter voltage/current
Hi,
I think it was Mike who pointed out that for best results, the circuit should be tuned so that the ac voltage and current seen by the tube are out of phase. Any one know of any online references on this kind of thing? I may be able to borrow an ARRL handbook from somewhere if the material is in there too.
Cheers
cv
Hi,
I think it was Mike who pointed out that for best results, the circuit should be tuned so that the ac voltage and current seen by the tube are out of phase. Any one know of any online references on this kind of thing? I may be able to borrow an ARRL handbook from somewhere if the material is in there too.
Cheers
cv
It'll be in the ARRL book, but buried in the antenna theory.
Look at transmission lines, impedance matching and standing wave ratio.
For best efficiency you need to build the thing as an AM radio transmitter, then the output is a Tesla coil style step-up transformer which drastically increases the voltage.
Impedance changes of the output (antenna) will be coupled back through the transformer and represented at the output device.
so the impedance matching effort should be continued right through the circuit. this is where things get very tricky....
As the plasma arc gets longer the "antenna" is longer and the tuning changes. You can envisage the "antenna" as a fuzzy area containing the last part of the tesla coil, the electrode, and throw in some interactions from the nearby grounded parts as well.
Let's just say it's impedance at a given frequency changes with arc length.
At a given frequency.... think about that....
this is why successful tplasma tweeters are self oscillating with a feedback pickup from near the output. they change frequency as it starts up and the arc grows. Hopefully following the resonance of the circuit as the tuned circuit changes as the arc grows.
Another approach would be to build a fixed frequency AM transmitter, then install a voltage and phase detector between the output transformer and last stage of the transmitter.
Feed the signals from the voltage and phase detectors into a comparator circuit and use the output of that to drive a variable coupling device in the transformer. I've worked on such a system which drives a goniometer (several shorted turns) around a shaft inside the air-cored transformer. On an AM morse code radio transmitter as it happens... The goniometer basically alters the tuning of the transformer/antenna/transmitter circuit allowing it to me tuned for maximum energy transfer.
I successfully drew an arc off the antenna terminal with a screwdriver, the tuning system adjusted itself into the new load, and I got morse code audio off the arc. There was barely enough range in the goniometer so for a plasma speaker application a different mechanical tuning methos might be better. A completely still humid atmosphere makes it easier and for a 100 watt RMS transmitter there were burn marks as evidence of sustained 4-6 inch arcs inside.... The slightest breeze would have disrupted these arcs. Don't think you can get so much without an enclosure.
So fixed frequency is possible, just very complicated. I can get a copy of the circuit if you wish. but remember it'll need to be used as a concept only because it's for a very different application.
Look at transmission lines, impedance matching and standing wave ratio.
For best efficiency you need to build the thing as an AM radio transmitter, then the output is a Tesla coil style step-up transformer which drastically increases the voltage.
Impedance changes of the output (antenna) will be coupled back through the transformer and represented at the output device.
so the impedance matching effort should be continued right through the circuit. this is where things get very tricky....
As the plasma arc gets longer the "antenna" is longer and the tuning changes. You can envisage the "antenna" as a fuzzy area containing the last part of the tesla coil, the electrode, and throw in some interactions from the nearby grounded parts as well.
Let's just say it's impedance at a given frequency changes with arc length.
At a given frequency.... think about that....
this is why successful tplasma tweeters are self oscillating with a feedback pickup from near the output. they change frequency as it starts up and the arc grows. Hopefully following the resonance of the circuit as the tuned circuit changes as the arc grows.
Another approach would be to build a fixed frequency AM transmitter, then install a voltage and phase detector between the output transformer and last stage of the transmitter.
Feed the signals from the voltage and phase detectors into a comparator circuit and use the output of that to drive a variable coupling device in the transformer. I've worked on such a system which drives a goniometer (several shorted turns) around a shaft inside the air-cored transformer. On an AM morse code radio transmitter as it happens... The goniometer basically alters the tuning of the transformer/antenna/transmitter circuit allowing it to me tuned for maximum energy transfer.
I successfully drew an arc off the antenna terminal with a screwdriver, the tuning system adjusted itself into the new load, and I got morse code audio off the arc. There was barely enough range in the goniometer so for a plasma speaker application a different mechanical tuning methos might be better. A completely still humid atmosphere makes it easier and for a 100 watt RMS transmitter there were burn marks as evidence of sustained 4-6 inch arcs inside.... The slightest breeze would have disrupted these arcs. Don't think you can get so much without an enclosure.
So fixed frequency is possible, just very complicated. I can get a copy of the circuit if you wish. but remember it'll need to be used as a concept only because it's for a very different application.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.