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Prune 5th March 2004 08:42 PM

I have come across a number of DIY designs on the net for driving the plasma tweeter corona, but they all seem more a proof of concept than engineered for hi-end sound. I'm looking for recommendations of which circuit to build, what tubes to use, etc.

Illusus 5th March 2004 09:16 PM

I'm in the same boat. If I had the time and money to thoroughly research the project I'd jump right on it. I did build a hastily constructed version of a design in AudioExpress(I don't remember which issue) It worked ok as a transducer, but not great, probably because I used junk parts and strayed from the original design so I could use what was on hand. Pretty cool nontheless. The fun part is using the corona to cut things.

P.S. I like your sig.

Alastair E 5th March 2004 10:12 PM

Plasma Tweeter
There were a couple on Ebay, in Germany earlier this week, They had a bid of around 600 sterling at the time if I remember rightly!

They used PL519 Line O/P valves, one per tweeter

I found them whilst searching for Pl519 valves!

audiobot 6th March 2004 12:02 AM

plasma plans

I built one of these last year. It was a great fun project. I used a sort of synthesis of Colin Joye's scheme and Ulhrich Haumann (they may both be misspelled). The EL/PL509 or 519 was the tube of choice for both and I think it is the tube that was used in the last commercial products. I screen modulated mine from the output of a small 6V6 PP fed through a line transformer run backwards to modulate the screen.

Anyway, I think the reason they are more like works in progress is that there are many ways and many tubes that would work fine. The secret is in the tuning of the coils and capacitance. That makes a huge difference in sound quality and efficiency. I emphasize HUGE. Until some one makes a standard tank circuit, and then it's not DIY, it will always be that way.

I do encourage you to try it, it is a cheap fun project. When you want to make it a permanent part of your system is when the real work will start. You will have to figure out a good shielding scheme for the RFI and build in the types of safety precautions that are necessary for a fire generating beast that runs on high voltage and current.

There is a lot of information to be gleaned from old patents if you want to search there. The original one, from 1952 or 3, used a pair of 807s. The 6146 have been used and I was thinking a 4-65 or 4-125 might make a good option. Read up on radio transmitters and vacuum tube tesla coils, they have a lot more in common than anything out of the audio world.

If you have any specific questions, ask and I will see if I can dig up my notes and literature.

By the way, they do sound incredible and it is on my short list of things to revisit.


fdegrove 6th March 2004 12:50 AM


Does anyone remember the old Ionovac units?

I think they used a 6DQ5...
Always noticed some hissing though and I hear the crystals didn't last all that long either.

Would nice to have a good one though...


Prune 6th March 2004 01:39 AM

Are plasma tweeters significantly better than good ESL panels?

audiobot, I don't have a specific question because my question is about getting started; all I do know is that I want to use them as tweeters in the speaker setup I'll be putting together this summer, so it's not just about playing around with HV (I already do this other ways :hot: ), but it's mainly about sound quality.
Certainly, if you do revisit the project, make sure to share your designs with us :)

BTW I was also thinking about the Ionic Cloud. Why not just put that kind of design in a sealed enclosure to avoid the ozone and nitric oxides problem? I seem to remember sealed chamber ESL speakers, althogh for a different reason (argon instead of air to prevent arcing, or something like that).

audiobot 6th March 2004 02:37 AM

sound quality
I've not had much experience with different ESL speakers. I will say the the plasma tweeter had a sound quality I have not heard before. In it's simplest form it is a pure point source and that does somehow seem to make a unique difference.

If you are familiar with HV work and have a variable power supply that can give you a 150mA or so, you should be able to knock up a working model in an afternoon or two. Then you can decide for yourself if it is worth pursuing to the extent of being able to add it into your system.

I didn't notice any problems with NO2 in the hundred or so hours I ran mine. Ozone production was a different story. It may seem funny, but when the system was tuned and playing the loudest, lowest distortion, etc the ozone production seemed to be at a minimum, almost indetectable and similar to one of those ionic air fresheners. Overall sound output level is a problem you will have to deal with, they are not power efficient to say the least. On the other hand I am judging from the standpoint of running them almost full range most of the time I was playing. If horn loaded, my rough experiments, they are loud, but lose the point source effect. I do think horn loading could be used to minimize ion migration as well, it that remains a concern with you.

I will try to dig out some old response files and maybe I can draw a schematic. Like I said though, it is a piece of cake to toss up a prototype. Probably some other people on the forum have had more experience with these than I have, though.


Prune 6th March 2004 08:04 AM

Re: sound quality

Like I said though, it is a piece of cake to toss up a prototype.
Yeah, but it's a good sounding prototype I'm after :angel:
If you have a good schematic, please post one, or comment on existing schematics such as

audiobot 6th March 2004 02:45 PM


As you can see at the following link this commercially available plasma tweeter is based on the EL519, so I would say a good sounding result is possible.

This site has a lot of good background and design info also.

I will try to find my drawings, they are not in electronic form so I will have to find time to convert them before they can be posted, and data sometime today. For now let me say, the plasma speaker/amplifier is fundamentally different, in my view, from other tube audio projects. It is a self oscillating Class C amplifier. As such, execution is everything. A picofarad here or there, which has little or no effect in the audio range, has a huge effect because you are working with a carrier in the MHz range. That means that in the abscence of a commercially available tank circuit, the coil must be tuned empirically. You can achieve excellent sonic results and the fact that there have been commercial products available show that the other obstacles (RFI, heat, ozone) can be overcome. But if you are unwilling to experiment this is probably not a project for you.

If you can get a high quality audio signal to the amp (transmitter)you can get quality out. My speaker sounded fantastic to my ears. The easiest and down and dirty way to do this that I found was to use a stepup transformer cap coupled to the screen supply of the EL519. The rest of the circuit in front of the 519 is just preamp, crossover and RFI protection, you can pick any design you want.

Colin Joye, who wrote the Audio Express article, believed that the best results were obtained with a low DCR coil oscillating around 27MHz. I have not seen the article, but I did have private communication with Mr. Joye prior to it's publication. Willis used a much higher DCR coil around 27MHz and also claimed good results. To me this just shows there are many paths to the same end. From my own experiments (from memory) I obtained the best result with a moderate DCR coil oscillating at a much lower frequency, 2-12MHz. I tried the 6CL6, per Mr. Willis' design, to drive the screen and it worked fine but I can't say it was vastly superior to the transformer coupling. The main thing is tuning the circuit so that the phase angle of current conduction is offset from the voltage phase angle such that the conduction takes place when there is no voltage drop across the tube. In early experiments I had the plates glowing bright red at only about 600V and 60mA. Later, with more tuning, I could pass 200mA with a plate voltage of over 700 and the tube seemed just fine with it. There is a technical article on the Svetlana site about using the EL519 as a radio transmitter that has some useful information.

I will warn you that my Radio Shack voltmeter was useless for measuring the circuit, turn it on anywhere near the thing and it would start switching from volts to amps to ohms and unknown modes, even turning off and on, all on it's own. I even had problems getting the SPL meter to work. This is of course with no shielding whatsoever, just experiments you understand. On the plus side, if you have a scope, all you have to do is hang a probe off of it and you will receive the signal. Very handy for checking modulation level, carrier frequency and watching for overloads on the transients of the audio signal.

If you want to try a really over the top design download the patents dealing with the Hill Plasmatronic. It was a masterpiece of design and dealt with the known problems of intermodulation distortion (which I did not really find to cause any objectionable effects) and ozone production.

It is a fun project and if you are willing to put in the time and thought you will end up with a truly unique speaker that few have heard and even fewer own. The only real downside is that if you don't finish the project, as I haven't, you will find it very hard to go back to an ordinary tweeter.


Prune 11th July 2004 07:19 PM

Re: plans

Originally posted by audiobot
If you want to try a really over the top design download the patents dealing with the Hill Plasmatronic.
I've been trying very hard to locate information on these, to no avail. The USPTO database only allows searching patents from 1975 onwards, and I didn't find anything. :bawling:
Does anyone here have schematics or other details, or at least know how I can find the related patents?

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