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Hi guys

I found your very interesting work on plasma tweeters and have some input that you might be interested in. I almost purchased a Plasmatronics Hill Type 1 unit in the US a few years ago, but chickened out (in part due to uncertainty about cost of gas in Norway, also space (and Ozone/UV) was a factor as well as the cash-flow situation of the time). I also have an aquaintance who owns what must be one of (if not the only one) few that was ever taken to Europe. In this email, I will try to add some information about that system because it is somewhat different from yours, yet quite similar.
So from memory:

  1. The design uses 5 electrodes fed from 5 tubes (that might in fact be identical to the tubes you are using, they were certainly "top hat" tubes as well)
  2. Each tube has a bias control
  3. Inert gas used is Helium.
  4. The 5 electrodes sit in a cavity which is about 2cm or so diameter. This cavity is ceramic.
  5. Each electrode has inert gas carried to it through a tube which sits outside the wire (carried along the wire as if it were the isolation material), or it might actually have been through the electrode -- in fact that is what I think it was. Hmmm.
  6. Crossover point is 700/1000Hz switchable. This was as far as the designers got the frequency response without running into space/cost/power/Ozone and whatever issues, although I believe that a few homes in California were built with integral lower frequency units (I want one!!!).
  7. Loudness is acceptable, but cannot remember how loud -- certainly not a problem
  8. Some crackle noise was present, appeared to be constant in loudness, but not a big deal when playing music.
  9. Separate tubed control unit/equalizer/active crossover was used.
  10. I don't think that a teslacoil was used -- I think it was direct drive ionic or perhaps HV transformer coupled. I don't know the modulation frequency either.
  11. The entire speaker should be thrown away and just the plasma section kept (which was small enough, but for the helium tank). Quite soft old and physically huge with space for integral huge helium tank, actually, but the plasma section was radical!

Another unit which you may not be familiar with is the one that took Nelson Pass out of commission for a while -- it was like an electrostatic unit -- flat transparent panel, but one of the problems was (I postulate) very large surface area of ionization which presumably created rather a lot of Ozone as well as radically low sensitivity. My aquaintance her in Norway had some contact with NP (he is a dentist) and shared this information with me. I also guess that the large aerial presented by the panels would piss FCC off like few other things!

If this is of interest, I might be able to obtain photos and possibly even schematics (well perhaps not, but who knows?), but that will have to take some time unfortunately due to my current state of "being on the move".

So, if you are at all interested, do let me know -- but I cannot promise on timing nor deliverables. My current projects (too many of them and all incomplete!) are also taking priority, so I cannot for the near future contribute to a design process. Then there is my new job and appartment finding process, so you know where I am coming from!

Petter (from Norway) New motto: Each man his own ozone layer regenerator, yeah!

the Plasmatronic (A letter from Malcolm Jenkins in response to Petter's letter above, 5/8/01)

A while back a guy in Norway (Petter, above) sent info on the Plasmatron. I found this in the October 1978 edition of Wireless World. It comes from a report on the High Fidelity Show in Atlanta and the Consumer Electronic Show in Chicago. The horn designer Jack Dinsdale was the reporter.
...."the Plasmatronic Hilltype 1 plasma driver, which claimed to provide exceptional clarity of reproduction, (zero colouration and laser-like phase coherence) from 700hz to above the limits of auability, and operated via a biamping system with a 12 inch sub-woofer and 5 inch mid-range unit. The plasma driver requires topping-up with helium svsilsble in cylinders from your local welding supplies company, every 300 hours of listening time. and the cost is claimed not to excede 30 to 40 cents per hour.
A picture of the Plasmatronic is shown below:

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