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Old 5th September 2008, 08:50 PM   #1
NeoY2k is offline NeoY2k  France
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Default Just an idea: Tubes and Class D

Hi everybordy,
I just had an idea:

Some valves/tubes exist that work in the RF band (and more).

What about doing class D with valves as it seems we have some problems with solid state, to try to run it at higher frequencies? Morover, these components are made for high power, and it may interest us.

I did not dig the subject. But I submit it to you. What do you think about it?

Nicolas
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Old 5th September 2008, 09:03 PM   #2
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Tube conduction losses make this impractical. Switching losses may also be large.
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Old 6th September 2008, 12:26 AM   #3
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Old patent:
http://www.google.com/patents?id=jtZ...BAJ&dq=3011025

Now what year is it again? 2008? Designing class-d with tubes would have what benefits?
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Old 6th September 2008, 02:31 AM   #4
Duo is offline Duo  Canada
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Now where's Sch3mat1c. He's done this.
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Old 6th September 2008, 09:44 AM   #5
NeoY2k is offline NeoY2k  France
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Thank you for the link
I don't know if it would have any real positive effect. But some can work at really high frequencies, and may not have the same problem that solid state has. I never said no problems or less problems. Just not the same.

So what if someone tried to make a very high speed class D amp, using tubes for that purpose?

Sch3mat1c has done it? I'll have a look at it
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Old 6th September 2008, 07:43 PM   #6
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Ya, seems to work okay. A class D-A style circuit gets apparently very little distortion (which, remember, is controlled by the PWM oscillator and comparator, no worrying about driver and output tube characteristics!) and excellent efficiency, as tubes go (potentially >80% plate efficiency).

Blasphemy, I'm sure

Results page:
http://webpages.charter.net/dawill/t..._Compound.html

I still have yet to try class D-AB, which should work fine, with the obvious advantage of better-than-terrible output network efficiency (50% of the output goes into that stupid resistor!), but with the disadvantage of needing a very linear transfer characteristic, particularly around the edges (notice the hysteresis and nonlinearity around the ends of the comparator's range above). Notice that class D-A PP is disasterous around screen-grid tubes.

Tim
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