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Old 5th July 2003, 10:16 PM   #1
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Question Need advice driving a tube

Hi,

what is the best way to drive a tube (getter???)

The tube is PL519 and needs 80V DC offset.

At the moment I have a transformer driving a simple transistor stage driving the tube.

Now it is not possible (?) to use a bridged Aleph-x or equal because the tube has only one 'input'.


Should I use a classA circuit with DC offset ?

Or better a bridged supersymmetric circuit and a transformer direct to the tube (How to get the offset ?)


Greets, Bernhard
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Old 5th July 2003, 10:44 PM   #2
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Hi,

Do you have a circuit drawing for that?

Quite a bit of solid state parlance for a tubeguy like me but I assume you want to provide a -80VDC bias to the controlgrid of that penthode?
Do you use it triode-strapped?

There are several ways to go about this, one of them is simply using a separate bias supply.

Keep in mind that tubes don't come in complimentary pairs so you'll need some trickery if you need a PP drive/output.
Here you can resort to a SEPP configuration as used in OTL amps, it's not perfectly symmetrical by nature but has the advantage of nulling any DC offset at the output...
But again you'll need a dual voltage rail of about +/- 170VDC.

This goes some way into tube territory but a lot of similarities exist in the sand amp field where often the same topologies are used.

Unfortunately I'm not familiar with the Aleph circuits but I'm willing to look into what you want to accomplish here and advise accordingly.

Cheers,
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Old 5th July 2003, 11:56 PM   #3
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Hi Frank,

there is a + 80Vdc offset on the middle grid.

The circuit modulates that 80V, the tube oszillates.

The higher grid is connected to ground and the lower is feedback for the oszillator.

Is there something I can do with that unused higher grid ?
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Old 6th July 2003, 12:04 AM   #4
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Hi,

Is the circuit meant to oscillate?


Cheers,
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Old 6th July 2003, 12:14 AM   #5
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Quote:
Originally posted by fdegrove
Is the circuit meant to oscillate?
The tube yes, but the circuit driving the tube is not of course.

The tube generates HF ( plasma tweeter )
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Old 6th July 2003, 12:54 AM   #6
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Hi,

All the circuits I know for these plasma tweeter were done completely with valves.

The ones I heard were always generating hiss, one way or another but...and that's the good news: I came across at least some other fellow in Germany who was working on something similar to yourself.

I'll be out tomorrow but if I can trace him, I'll let you know.

Cheers,


P.S. I used to live in Muenchener Freiheit.
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Old 6th July 2003, 04:43 AM   #7
Vaihde is offline Vaihde  Finland
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http://www.plasmatweeter.de/
http://www.ee.vill.edu/~cdanjo/sitemap.html

there some plasma tweeter links
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Old 6th July 2003, 08:13 AM   #8
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Yes, I know all the links, my question is:

is there a way to use a bridged amp without using a transformer ?
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Old 7th July 2003, 06:17 PM   #9
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Interestingly, I have had good luck driving plasma type
tweeters using a high voltage tube to cascode the
smaller Mosfet which serves as the actual gain device.
The Source of the Mosfet goes to ground, the Gate forms
the input pin, and the Drain goes to the Cathode of the high-
voltage high-power tube. The Grid of the Tube is biased at the
appropriate DC value, and the arc of the plasma is driven
by the Plate of the tube. Worked great on Plasmatronics,
and had quite a bit lower distortion than other approaches,
and also better reliability.

This approach is also really effective in driving electrostatic
loudspeakers....



ps. This approach operates great without a transformer,
bridged or unbridged.
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