tubes in Class D?

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#21
beamnet said:

I think that pists about the use should be avoided: Tubes obviously have no big beneficial propertys for class D. This is all just for fun...

If you have ever seen a mercury vapour rectifier, you know why it's such fun. I don't know if thyratrons give a big show, but, as they are filled with gass, i guess they will.

Bas
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I find this is more than fun. It could make ESLs interesting for large scale applications (probably much cheaper than Neodymium wasting large scale magnetostats).
 
#22
well, i started this, but have neither teh financial flesh to do this, nor a pair of esl's

I have some smaal tubes lying around to make the sawtooth, and maybe even the comparator stage and could afford to buy two thyratrons, but then there comes the ingredient time and knowledge..

for thos einterested: i found out that small thyratrons are extremely cheap. especially russian valves. I work with Russian valves a lot and have NEVER been disappointed with their performance..


BAs
 
#27
Ignatrons and their various cousins are just to slow for this task. maybe you could strech the performance enough to run a sub-woofer but I have my doubts.
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I don't know about ignitrons but hydrogen filled thyratrons are fast enough, actually one of the main reason why they are still used at very high power level applications is that they are much faster than any solid state equivalent switch. I spent a minute searching by Google and came up with thyratrons that are able to switch 500KA/ps, is that fast enough!

A thyratron is very similar in operation of a SCR so in order to turn it off the voltage over it must drop to zero, there should be no problem to accomplish that by using 2 of these driven in push pull but connected in series as in ordinary power amp, another way is to use 4 of them in a bridge. Inverters for industrial applications have been built with these devices so it should not be a big problem to make a class D amp which is very similar in design.

Anyway this is mostly just of academic interest for any power level except for the extremely high, a tube based class D amp would have much less efficiency than one built with solid state, but maybe if you want to build a class D in the MW range....

Regards Hans
 
#29
I find this is more than fun. It could make ESLs interesting for large scale applications (probably much cheaper than Neodymium wasting large scale magnetostats).
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It would be fun to see such a thing arc in windy conditions. 😀

Fun aside: The only application of a tube class-d I can imagine would be the modulator stage of a large AM transmitter.
Low-voltage and low-power applications would be for fun only.

Regards

Charles
 
#30
I remember thyratrons now. Looked into how they worked in light dimming circuits. Since they work like an SCR, wouldn't you have the same trouble building a swtiching amp as with an SCR. How do you turn it off?

Why not use more convetional tubes? All you want to do is produce a nice 500kHz-1MHz square wave at modest power, without killing the tube. Shouldn't be hard, right?
 
#33
phase_accurate said:


It would be fun to see such a thing arc in windy conditions. 😀

Fun aside: The only application of a tube class-d I can imagine would be the modulator stage of a large AM transmitter.
Low-voltage and low-power applications would be for fun only.

Regards

Charles
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Modern day transmitter powerampifiers use large tubes in class c configuration (icw a nice filter)

(thats what i've heard)

they shut be useable for class d audio amplifiers??
 
#34
You are basically right about the class C operation. But the AM modulation is done via variation of the plate voltage of the output stage which needs onehellufanaudioamp.

Though there are other methods than PWM that allow efficient AM modulation.

Regards

Charles
 
#36
You need to invent Zero Voltage Switching class D topology first... the real Hiten Mitsurugi-Ry¨± thing.

p.s. Are there any people doing class D with IGBT?

For a MW design, maybe IGBTs for Shinkansen, TGV or ICE high speed trains are suitable for the job. These engines usually have a maximium power of 4~6 MW, powered by a 3-Phase SPWM inverter.

tubetvr said:


I don't know about ignitrons but hydrogen filled thyratrons are fast enough, actually one of the main reason why they are still used at very high power level applications is that they are much faster than any solid state equivalent switch. I spent a minute searching by Google and came up with thyratrons that are able to switch 500KA/ps, is that fast enough!

A thyratron is very similar in operation of a SCR so in order to turn it off the voltage over it must drop to zero, there should be no problem to accomplish that by using 2 of these driven in push pull but connected in series as in ordinary power amp, another way is to use 4 of them in a bridge. Inverters for industrial applications have been built with these devices so it should not be a big problem to make a class D amp which is very similar in design.

Anyway this is mostly just of academic interest for any power level except for the extremely high, a tube based class D amp would have much less efficiency than one built with solid state, but maybe if you want to build a class D in the MW range....

Regards Hans
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#37
Originally posted by tubetvr I don't know about ignitrons but hydrogen filled thyratrons are fast enough, actually one of the main reason why they are still used at very high power level applications is that they are much faster than any solid state equivalent switch. I spent a minute searching by Google and came up with thyratrons that are able to switch 500KA/ps, is that fast enough!
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Not really that helpful a post, the current rise times you quote are for megawatt thyratrons so even thought the rate seems high, as a percentage of power handling it's just not that special. But the real rub is at the other end to the current pulse, the one where you need to turn it off and then the minmum on time and hold off time. These new thyratrons are so improved they can actually be used at speeds in excess of 20KHz 😱.

20KHz are you kidding me? A decent class D amp needs 200KHz at least and prefferably 2MHz. I mean I know this thread is largely tongue in cheek, but there are newbies filing away information for future use :cannotbe:.

In anything but megawatts, laser drivers even high power radar, solid state switches have replaced these tubes. Another problem is turn on and turn off delays which vary with temperature, age and current density. These devices are just a poor (not impossible) choice for variable pulse width high speed swtching. Especially in a design where either on or off time approaches zero.

To deal with their speed limitations you would have to design a multi-phase switcher, maybe ten of them effectively in parallel, each with a slower clock and a phase offset. The good news is that you could sell a "multi-phase hydrogen filled thyratron modulator" to any Sci-Fi movie 🙂 .
 
#38
hermanv said:

....The good news is that you could sell a "multi-phase hydrogen filled thyratron modulator" to any Sci-Fi movie 🙂 .
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Or tube fanatic 😀 Apparently someone did use a tube output stage on a class d amp, they were posting about it hear a few months ago.... not like I've seen it though, haven't seen them post about it in awhile either.

I don't know much about tubes but I figure there's a few reasons (like those you've mentioned) why class d had to wait for a decent mosfet to evolve.

Regards,
Chris
 
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