# Amplitude modulated 27Mhz RF amplifier for Plasma Loudspeaker

Discussion in 'The Projects Forum' started by thadman, Apr 8, 2010.

Apr 8, 2010
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I'm interested in building a plasma loudspeaker using a 1kW amplitude modulated RF amplifier. The amplifier will modulate the output of a 27Mhz RLC circuit (HV vacuum tube capacitor + air core transformer) which is connected in series between two Tungsten electrodes (opposite polarity). I believe if a potential of 30kV/cm is placed between the electrodes, dielectric breakdown of the air will occur and plasma will form. Electricity will then be conducted through the plasma. If we modulate the 27Mhz resonance, we can vary the size of the plasma rapidly to produce sound in the audio bandwidth. We desire a stable plasma, which may allow us to assume a Maxwellian distribution.

I'm interested in purchasing a quantity of Russian military surplus vacuum tubes for the amplitude modulated 27Mhz RF amplifier. How can I evaluate the power and fidelity of the tubes or differentiate between them? I'd prefer a minimum of 1kW.

For a stable plasma to be assumed, a "holding current" must be maintained. How can I calculate this? The holding current will place a constraint on the widest possible air gap that will support a stable plasma if I have a limited amount of power.

The holding current will have a significant influence on the required power.

Here is a list of Russian military surplus vacuum tubes that are available for broadcast.

If you are familiar with any of the models, I would greatly appreciate a recommendation.

If we directed helium gas towards the electrodes, how much would this effect dielectric breakdown? How could I calculate the distribution of air and helium? Would it be possible to calculate ozone production?

Is infinite electrical conductivity a poor assumption for the plasma?

How can I calculate the pressure field (ie acoustic field) created by modulating the resonance by varying the current? How can I calculate the percentage of electrical energy that is converted to acoustic energy?

Thanks,

Last edited: Apr 8, 2010

Apr 20, 2004
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3. ### retched AAC Fanatic!

Dec 5, 2009
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Well, it seems you have your plate full. In about 26 years, when your done with all those calculations, we can talk about plasma as a loudspeaker.

I am guessing you are either very wealthy or well backed, because making a plasma loudspeaker is a very inefficient way to broadcast sound.

The amount of power required for the same amount of amplification as a standard loudspeaker is on the order of magnitudes.

However, it would look real cool.