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 😉
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 😉
beamnet said:
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.
😉
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
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
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?
Somewhere I recall that some gaseous lamp dimmers were high frequency. I wonder if some old circuit could be adapted?
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).
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.
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.
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.
And are still used where extremely high power and fast switching times are needed. Thyratrons, ignitrons and so on...el`Ol said:
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
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
Of course it is possible to make a class D amplifier using tubes, bandwidth is not a problem and there are many easy available tubes that can handle 100's of MHz with high power.
However I doubt that it would be possible to make a class D tube amp as efficient as one with transistors, the main problem is that tubes work more like FETs with soft saturation that need quite high rest voltage to lead any current, the end result is that there will be a quite high power dissipated in the tubes.
As have been said before there was and still are some Thyratrons available for switching very high powers, like 100's of kW and some of these have the ability to switch very high power in very short time, like 20ns, they also have the advantage of having low rest voltage so they would improve efficiency compared to using ordinary tubes.
From a parts catalogue about hydrogen filled thyratons "Metal-ceramic construction thyratrons are rated at I to 100 KV, can switch at rates up to 500 KA/ps, 20 to 20 KA at average powers to 1.0 MW"
The problem is probably to find a hydrogen thyraton that is of reasonable size for use in a domestic audioamplifier.
Regards Hans
However I doubt that it would be possible to make a class D tube amp as efficient as one with transistors, the main problem is that tubes work more like FETs with soft saturation that need quite high rest voltage to lead any current, the end result is that there will be a quite high power dissipated in the tubes.
As have been said before there was and still are some Thyratrons available for switching very high powers, like 100's of kW and some of these have the ability to switch very high power in very short time, like 20ns, they also have the advantage of having low rest voltage so they would improve efficiency compared to using ordinary tubes.
From a parts catalogue about hydrogen filled thyratons "Metal-ceramic construction thyratrons are rated at I to 100 KV, can switch at rates up to 500 KA/ps, 20 to 20 KA at average powers to 1.0 MW"
The problem is probably to find a hydrogen thyraton that is of reasonable size for use in a domestic audioamplifier.
Regards Hans
would this one work @ $19.95 on ebay?
http://www.mif.pg.gda.pl/homepages/frank/sheets/137/4/4C35.pdf
http://www.mif.pg.gda.pl/homepages/frank/sheets/137/4/4C35.pdf
class d aims to increase effeciency and decrease the size.
coupling them with tubes will defeat the purpose.
but it will make for a nice experiment.lets see what comes out.
coupling them with tubes will defeat the purpose.
but it will make for a nice experiment.lets see what comes out.
raintalk said:
Interesting schematic. Tripath make driver chips for external mosfets. You might be able to start there and use tubes for the outputs instead. The output transformer could be tricky.
A fun idea. 😎
Hello,
I just wounders... In a normal tube amplifier you have to bias your tubes to have an idle current, but in a class D it might be a good ide too set the bias so you only have a few µa trouh the tube, since it just going to be on/off any well. That way we can save a lot of wasted power(In a 50 amplifier that will say about 40w saved!), what do you guys think about that?
Best regards,
Magnus Kofoed
I just wounders... In a normal tube amplifier you have to bias your tubes to have an idle current, but in a class D it might be a good ide too set the bias so you only have a few µa trouh the tube, since it just going to be on/off any well. That way we can save a lot of wasted power(In a 50 amplifier that will say about 40w saved!), what do you guys think about that?
Best regards,
Magnus Kofoed
I think tha't quite a good idea. However, you would not omit the bias, you'd just make it very high. I'm not quite sure how this works with thyratrons. They seem to have no big quiescent current.
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
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
Did some more research.
These thyratrons work like thyristors.
They need to get their anode voltage below theur firing voltage to shut off. This might be tricky...
Bas
These thyratrons work like thyristors.
They need to get their anode voltage below theur firing voltage to shut off. This might be tricky...
Bas