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Old 11th December 2005, 04:47 PM   #1
beamnet is offline beamnet  Netherlands
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Default tubes in class d?

Hello there,

I am looking at class D amps and wonder:

"Could i use tubes?"

It seems like it would make tubes unsuitable for analogue audio worth a try in class d...

Output using tubes i can see, maybe even the ocillator?

Bas

Oh, and i am not into tubes because they sound good, i am into tubes because they are cool
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Old 11th December 2005, 07:12 PM   #2
Pano is offline Pano  United States
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Default Re: tubes in class d?

Quote:
Originally posted by beamnet
"Could i use tubes?"
Don't see why not. I used to work in a theater that used tube dimmers. Low switching frequency, to be sure, but very high power. You'd have to find tubes that can switch fast and handle a bit of power.

So come up with a circuit for us! I may not be pactical, but it might be fun.

BTW, tubes aren't cool- they're hot.
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Old 11th December 2005, 07:25 PM   #3
poobah is offline poobah  United States
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use RF tubes... whole new line of thinking...
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Old 11th December 2005, 07:45 PM   #4
beamnet is offline beamnet  Netherlands
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That's what i had in mind...all those rf tubes lying around...

I am a total zero on class D

I could not even begin to think about making a circuit

The easiest way would be to just adept an output stage for tubes..

Bas
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Old 12th December 2005, 04:42 AM   #5
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This would definitely be a fun thing to do!

Somewhere I recall that some gaseous lamp dimmers were high frequency. I wonder if some old circuit could be adapted?
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Old 12th December 2005, 04:52 AM   #6
el`Ol is offline el`Ol  Germany
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I read somewhere that switching tubes were used in high-power, high-voltage applications before the IGBTs were invented (which are very slow and not suitable for switching).
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Old 12th December 2005, 06:24 AM   #7
hermanv is offline hermanv  United States
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The advantage of class D designs is efficiency. To make class D sound good requires some extraordinary effort. Since tubes can not saturate the efficiency is mostly gone.

Switching frequencies of at leat 1 MHz with a current of say 5 Amps to have any useful power.

It would be difficult if not impossible to use a transformer (high degree of DC imbalace) so an inductor impedance match would be neccessary. To do it right you need to drive both positive and negative directions so you need one of those PNP tubes, alternatively you bias the speaker up at some positive voltage leading to a whole other set of problems.

None of this is impossible but about now it should be starting to sound like it's not the best idea ever conceived.

For this much effort a first class conventional tube amp could be built. There's nothing wrong with that as it takes advantage of the tube being a transconductance devide instead of a current mode device.

If you just want to drive high currents with vacuum tubes, then consider an OTL amp.
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Old 12th December 2005, 09:06 AM   #8
IVX is offline IVX  Russian Federation
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The major benefit of the tubes is better linearity ( many other properties is worse), but if they will work like switch ON/OFF only, the linearity will not so important.
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Old 12th December 2005, 09:12 AM   #9
mzzj is offline mzzj  Finland
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Quote:
Originally posted by el`Ol
I read somewhere that switching tubes were used in high-power, high-voltage applications before the IGBTs were invented (which are very slow and not suitable for switching).
And are still used where extremely high power and fast switching times are needed. Thyratrons, ignitrons and so on...
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Old 12th December 2005, 11:09 AM   #10
beamnet is offline beamnet  Netherlands
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cool, some good response.

a few things

- a HAVE a huge 70+watt puspull tube amp.

- I never implied it was a sane thing to do

- except for the output, lots of other tasks could be done with tubes.
I seem to recall tubes that can function like comparators, but i don't know whee i saw that..

pnp tubes..... there's no such thing

can't you just use a normal (or even limited bandwidth, to cut off any hf) pushpull OPT? My guess is that it would filter the 1mHz quite adequately..


Bas
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