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Old 9th March 2008, 07:00 PM   #111
p3142 is offline p3142  Germany
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The right 811 does not have 100uH chokes in the heating supply. Is this a drawing error?
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Peter
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Old 9th March 2008, 09:16 PM   #112
OzMikeH is offline OzMikeH  Australia
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Impedance mismatch between the two stages?
you need to show the output inductor as well. and probably take your positive feedback from the final output. the frequency changes as it starts up for better drive, this is intentionbal, because the load changes as the arc flame builds. think of it as self tuning for max power by changing freq.
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Old 9th March 2008, 09:22 PM   #113
Serge66 is offline Serge66  Switzerland
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How about removing the 0.1uF caps between ground and filament heaters/cathode?
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Old 10th March 2008, 02:42 AM   #114
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Quote:
Originally posted by angsuman
Hi George, I'm not trying to threadjack or anything, but I'm at my wit's end trying to get my plasma tweeter to work and since your email seems to be disabled I figured I should ask my question here. What I'm trying to do is make essentially the same circuit that everyone does with a screen driven pentode, but then use an 811A linear amplifier to get more power. I have a schematic that is located at this link.

http://www.flickr.com/photos/1403176...39128/sizes/l/

anyone please feel free to comment on it, whether it is even possible or not to do what I'm trying to do.

Thank you.

Ok, if ur going to mess around with relatively high power tubes, you should know what you are doing first.

There are several errors in your schematic.

I'm more concerned about the high power level you will have there, IF it works - if you do not thoroughly shield this device, you will be making SERIOUS levels of RFI. In the USA, you'll be operating a radio transmitter without a license, and liable for some serious penalties if some local ham hears you and finds you, tells the FCC... Be sure to be extra special careful to DOUBLE shield everything.

YOU CAN NOT MAKE IT LOOK PRETTY by having those nice tubes glowing on top of a chassis!! IT HAS TO BE SHIELDED FULLY!!

[beats horse to death...]

Also keep your hands OUT of the thing once it is wired up.
The 1200vdc is DEADLY!!

RF burns hurt a whole lot too...



EXCERCISE EXTREME CAUTION!!
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Old 10th March 2008, 04:55 AM   #115
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Yes I understand the dangers involved and we're doing this under the supervision our physics teacher who has much experience around high voltages and we do shield the whole structure with a faraday cage.

Yes the 100uH chokes are an error from an older schematic really its a simple bifilar wound choke we wound on a ferrite core and about 12 turns of wire.

I have added an impedance PI matching circuit between the 807 and the 811A tubes.

OzMikeH: What do you mean I have to show the output inductor as well?

I thought I was taking positive feedback from the final output at the hot end of the Tesla coil?

Serge: I thought I would need the two 0.1uf capacitors across the heaters to keep the AC filament hum out of the signal?


Thank you everyone for your responses.


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Old 10th March 2008, 05:13 AM   #116
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Quote:
Originally posted by bear
PLEASE PLACE A FULL COVERAGE GROUNDED SCREEN AROUND ANY PLASMA TWEETER!!
This is ONLY needed in RF-powered plasma, and you really shouldn't be putting RF near your audio. DC is the way to go, and has historically produced the best results.
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Old 10th March 2008, 03:38 PM   #117
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Quote:
Originally posted by abzug

This is ONLY needed in RF-powered plasma, and you really shouldn't be putting RF near your audio. DC is the way to go, and has historically produced the best results.

Ummm... do tell??

What commercial "DC" plasma speakers are there?
All of the famous ones I know of are "RF" type - the Ionovac and Ionofane being the most famous back in the 50's...

All of the commercial plasma speakers, like the Acappella, today are well shieded, look at the enclosures?

The only DC based HV plasma speaker I know of was Gerald Shirley's "Corona Wind Loudspeaker" from the JAES in the 50's...

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Old 10th March 2008, 03:49 PM   #118
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Quote:
Originally posted by angsuman
Yes I understand the dangers involved and we're doing this under the supervision our physics teacher who has much experience around high voltages and we do shield the whole structure with a faraday cage.


I'm still concerned, did the physics teacher "approve" the schematic?? If so, I'd not have much confidence in his knowledge of HV & RF circuits...

Since you do NOT need such power to make a working plasma tweeter - as shown here by George - why then are you trying to pump up the power levels??

Quote:
Yes the 100uH chokes are an error from an older schematic really its a simple bifilar wound choke we wound on a ferrite core and about 12 turns of wire.

I have added an impedance PI matching circuit between the 807 and the 811A tubes.
What is the impedance at the cathode of the two 811As?
Can you measure it?
Calculate it?
How do you know that it is what it calculates out to be?

Quote:
[OzMikeH: What do you mean I have to show the output inductor as well?

I thought I was taking positive feedback from the final output at the hot end of the Tesla coil?

Serge: I thought I would need the two 0.1uf capacitors across the heaters to keep the AC filament hum out of the signal?
Think about it some more... what type of amplifier is that?
How does it work?
And how much drive do 811As require in this configuration?

You should have an ARRL Handbook and a W6SAI Bill Orr "West Coast Handbook" at your side for this...

Quote:
Thank you everyone for your responses.

One of the keys do doing design is asking good questions, and then finding the answers...

_-_-bear

PS. I have emphasized the need for shielding and a good faraday cage because this is a DIY forum, and this little detail might not be otherwise noticed or even known by many...
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Old 10th March 2008, 11:12 PM   #119
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Yeah I understand, I'm here to learn. It's essentially in the design phases, my physics teacher does not have much knowledge of circuits because he's a mechanical engineer by trade. However I did get the schematic approved of, or at least showed to Max Robinson, at www.funwithtubes.com. He told me that the input impedance of 811A tubes at the cathode was about 200 ohms. And I designed a PI matching circuit with that knowledge. He also recommended an ARRL handbook which I'll probably look into. The reason why I want more power into it is to try to lower the cut-off frequency. I'll go learn more about radio frequency amplifiers, I already have much experience with audio amplifiers and loudspeakers but I guess I have lots to learn about radio.
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Old 10th March 2008, 11:17 PM   #120
Serge66 is offline Serge66  Switzerland
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Angsuman,
You are driving your 811 by the cathode (the grid being grounded).
The signal coming from the 807 is shorted to ground through these caps.
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