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Old 8th October 2007, 02:10 AM   #1
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Default Plasma Tweeter

Hello everyone, I'm building a plasma tweeter as a school science project. However I don't simply want to rehash a previous schematic.
I've looked at Goerge Green's plasma tweeter and it seems like a very good starting point.

Plasmatweeter

Now my current problem is I'm not sure which tube I should start with for the oscillator section, everyone seems to really like the 6L6 as their oscillator but I'd like to try out an 811. Can anyone offer any advice
for what would be the best choice?
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Old 8th October 2007, 09:06 PM   #2
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Which school in LV?

Cyclotronguy
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Old 8th October 2007, 11:05 PM   #3
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Palo Verde High School

are you from Vegas?
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Old 8th October 2007, 11:49 PM   #4
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Yes, was associated with DoE and DRI.... Lived out off N. Jones; back when Rampart was just a dirt road.

Soooo you going to have something built by Jan 08? IF so you need to bring it by CES.

Cyclotronguy
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Old 9th October 2007, 12:59 AM   #5
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DRI that's Desert Research Institute, yeah my dad is a professor at UNLV. I might have the project done by Jan 08 the fair is in March so hopefully I'm successful. Do you have any experience with Plasma tweeters or Vacuum tubes?
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Old 9th October 2007, 05:13 PM   #6
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Yes, but typically not little ones. My last adventure in vac tubes were ones you could unbolt and stick your head and shoulders inside while changing filaments or soldering up water leaks. Vac inside the tube was acheived by turbo pumps, backed by DP's backed by roots blowers.

Made a number of flame speakers back in my youth as well as plasma. It all started off with an old scientific american article on ben franklin's flame speaker... and electrit motor driven BBQ spit. Interesting read BTW, guessing that article was circa 1966.

Fist came the oxy/ gas flame seeded with KCl driven right off the plates of a mil surplus tube radio (R4-ARR2 or BC 455). That was the late 60's and HV electronics were cheap and easy thanks to govt. surplus. Old dynamotor driven "Command Receivers" at $5 each formed the basis of many a project.

Later came the plasma tweeter, oscillator was a 6v6gt, modulated directly with way too much DC on the plate; but hey tubes were cheap. That fed a TV "flyback" transformer to get the high voltage. Played with different gasses: atmosphere, N2, Ar, He.

Eventually wandered off into really big tesla coils driven by Eimac transmitting tubes.

In any regard, the electrodes were thorated tungsten from the local welding supply in water cooled holders.

Very likely that I have schematics somewhere..... will dig around this weekend and see what I still have on file.

Cyclotronguy
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Old 10th October 2007, 12:06 AM   #7
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That's pretty cool. As far as tubes go the power supply I designed gives about 720V of B+ I can't really spend that much more on the power supply because I'd need to increase the voltage handling of the capacitors. I could wire my transformer to give about 1400V B+ but I'm not too confident with that. So working with 720V B+ I was wondering which tube I should begin with for plasma tweeter experiments.
The 811 seems pretty affordable but it also seems to want more plate voltage. I've built tube amplifiers before but I don't really have a clue about radio circuits so I'm split between using an 811, which is a transmitting tube or a 6L6 which is what it seems everyone else uses in their plasma tweeter projects.

http://www.mif.pg.gda.pl/homepages/f...049/8/811A.pdf

http://www.mif.pg.gda.pl/homepages/f.../021/6/6L6.pdf

I'm curious if anyone could offer any input on why people use a 6L6 tube what properties of this tube are desirable in this application.

Thank You.
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Old 10th October 2007, 02:07 AM   #8
eyoung is offline eyoung  United States
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Default tubes

look at el 34 tubes they have much higher (forgiving plate voltages or kt88 or 6066 all have same pin outs)
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Old 10th October 2007, 05:10 AM   #9
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From what I've seen EL34 type tubes are quite expensive I guess because of their demand in tube amps. I found 811 tubes for $12 each and 6L6 for $8 each. The main issue I'm worried about is the direct heating of the 811 as it seems a bit finicky.
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Old 24th October 2007, 11:52 PM   #10
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So I got my teacher to approve my parts and he will order them soon. However one issue still confounds me. All the plasma tweeters I see use a beam tetrode and modulate the screen and put feedback into the grid. For example in this post,

http://www.diyaudio.com/forums/showt...35#post1147435

there is capacitive feedback from the anode to the grid. However, if I'm using directly heated 811 tubes would I put this feedback to the grid of the tube? or back into the cathode?
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