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VTTC Plasma Tweeter

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EDY19

Sun Dec 30 2007, 04:37AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

Well, here it is - my new project (as if i didn't already have enough!!

) Its a replica of Ulrich Haumann's plasma tweeter, with an EF86, ECL82, and an EL519 or 6KG6A tube. The transformer is home wound- used to be a 24V 8A secondary, but i rewound primary (20AWG) and secondary (26AWG) for a dual 250V secondary (put in parallel and used with voltage doubler for 6KG6 tube plate supply). In order to count the turns, I used my coilgun optical sensor wired up to pulse every time the form rotated one revolution, and wrote a program for a microcontroller to count the pulses and display on hyperterm on my computer. The front switch is switched to the left to turn on filaments to all three tubes, and then switched to the right in order to activate plate supplies. Input is from an RCA jack on the front, and the two knobs are flame adjustment and volume for the audio. The smaller transformer is the filament transformer for all three tubes. I figured this way the plate supply will be independent from the filament currents so the filament voltage doesn't sag. As soon as i find a EL519/6KG6A/EL509 or similar on ebay, I'll be in business!
(The tubes in the picture are not the correct tubes, but the right ones are sitting at the post office downstate, i just wanted some tubes there for looks

)

Mates

Sun Dec 30 2007, 05:19PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

I'd love to see (hear) it playing...
Do you plan any "focusing" of the sound or you leave it omnidirectional ? What about the ozone problem - when you keep it playing in the living room for few hours? And the sound quality - is it really so good?

Thanks for answers...

EDY19

Sun Dec 30 2007, 05:40PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

I don't plan on leaving it operating for hours, so I'm not too worried about ozone. I'm going to leave it omnidirectional for the time being, and I'll let everyone know about the sound quality as soon as I find a power tube for it!

Dr. H.

Tue Jan 01 2008, 02:18PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

I don't think that the ozone will be such a problem. They produce very little ozone and if you are so worried just open the window for 5 min end it is gone. I am also looking forward to see it working and to see your opinion about the sound. I have been looking on those things for long time and i want to meka one but never had the time. Keep up the good work

Cheers Huben.

EDY19

Sat Jan 12 2008, 12:31AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

The tweeter is up and running!

It sounds pretty good, the only noise is from the homewound transformer buzzing a little bit- I also plan to rewind the secondary coil, since it is on a polypropylene form and it gets quite hot. The tube runs well though with the smallest flame, and that is where the audio sounds the best, directly from my computers headphone jack. The flame is adjustable from about 3mm to 1cm. I want to try some other brand preamp tubes, but i'm not sure how much difference this will make so I am hesitant- for the preamps, i bought some reallly cheap svetlana tubes (the cheapest I could find just for testing) Do you think NOS tubes would improve sound much? The 6KG6A tube I bought is a RCA tube, and it is working like a charm

Suggestions welcome!!!

Tonskulus

Tue Jan 15 2008, 05:16PM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

Nos tubes does nothing really noticeable for soundquality. Its just all in your mind. Anyway, good to hear its up and running well. You can rewind the secondarycoil so that there is no form at all, just air. Its easy if using thick enough conductor.

I made plasmatweeter few years ago and I was impressed about its soundquality. Nice and clean sound from plasmaflame..its just sounds unbelieveable. I also noticed that it made lots of RFI around my room. It was possible to get RF burns out of metallic objects placed few feets away. So good RF shielding is necessary.

So, next step would be plasma subwoofer? :)

EDY19

Tue Jan 15 2008, 05:20PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

Well, got a NOS Sylvania tube, and the flame is able to get up to 1.5cm long now

The audio was kinda noisy, so i replaced the cable from the volume pot to the EF86 with a shielded cable, and that problem is much better now. Also, i found the bias on g2 of the EF86 was much to high- around 160V instead of 100, so i added a 330k+58k resistor, and the bias is now much closer to 100V. This lets me put more volume on the tube without it reaching distortion, and the flame size shrinks considerably when there is no music playing. My homewound transformer hardly gets above room temperature, but I still have to rewind the secondary on something heat resistant. While replacing one bias resistor, i accidentally disconnected completely the g2 voltage, and the flame was COMPLETELY silent, so I figured the noise was coming from that tube, hence the shielding. Once i rewind the secondary with some thicker wire and a heat resistant form, i'll update once more

Every once in a while, my printer or TV will turn on when i first turn on the tweeter, but that seems to be the extent of the RFI =-O

Marko

Wed Jan 16 2008, 02:25PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Are those few turns at top of the pipe all of a coil you are using?

Any idea of frequency you are running at?

In your place I'd try to use some really fat wire and bigger former to reduce heating.

I's also rather use cardboard tube instead of PVC because it's more resistant t heat, and to make it really though you could pour epoxy resin into it.. maybe fix a nice breakout point into the resin too :)

That is if you don't have anything like teflon or ceramic tubes.

Cool work as of now sir, keep up.

Marko

EDY19

Wed Jan 16 2008, 02:52PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

I'm using about 15 turns for the secondary coil, with an Fres in between 30-45MHz. Hence the heating in the wire

If i turn the flame up, my copper electrode melts, so if anyone has and ideas about connecting a tungsten welding rod to the new (and thicker - 14ga.) secondary? I also thought about using cardboard, but the rest of the project looks so nice- and cardboard doesn't quite float my boat

Edit: I used some 14 gauge wire and wound with 17 turns (same as the last coil) and for some reason there is a lot of noise in the flame now. Tried removing some turns, but still making lots of noise... ? Anyone know why this might be?

EDY19

Thu Jan 24 2008, 03:37PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

Thought some people might want a video - the audio from the camera microphone is awful, in real life i promise it sounds crystal clear!

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