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In Reply to: RE: Circlotron with MOSFET output posted by Banat on December 09, 2011 at 12:14:03
My friend is working on same type of amplifier and he just sent me a link of the circuit from Paul Hynes, what do you think? Obviously, I can have tube as driver stage via 1:1+1 interstage transformer, what about 45 or 300B?
Follow Ups:
Mr Paul Hynes SS Fet Circlotron circuit is basically correct , but need bias circuit for output Fets which is not present on schematic from your link ! , it could be driven with small SET for sure , but I think that tubes 45 / 2a3 / 300 b is not appropriate for this application since the power MosFet devices usually need only few Miliwat for full gate charge/disharge control.
Still I think that hybrid design from Mr.Andrea Ciufolly (Audiodesign) is the right one !, to rise the desired output power is enough to add few more 2SK1058 devices in parallel .
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Enlightened Evolution-Astral Projection
Hey! What about 6C45 tube as driver?
Yes 6c45p tube is OK for that position ( I strictly refer for use in Mr.Ciuffoly original hybrid Circlotron design ).
Few remarks :
6c45p tube have enormous high coefficient of gain ( 52, + - 16 ) ,and originally is used for Russian military Radar RF equipment so is very prone to oscillation in RF VHF/UHF spectrum if is not used properly in Audio application , special when is connected as Anode Follower SET driver like is done in the original Mr.Ciufolly design .
So the grid stop resistor connected near as possible to tube socket is mandatory , and some small value 100Pf/1KV capacitor connected in parallel with driver transf. primary coil is good to for prevention of oscillation in RF range .
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Enlightened Evolution-Astral Projection
Edits: 12/12/11 12/12/11
My friend yesterday has recommended I have the Kevin Kennedy 26 circuit (incl;uding the whole power supply circuit) as the driver for the Paul Hynes circlotron MOSFET output circuit.
The only thing as this 26 circuit for the driver is switching the line output transformer to a proper interstage transformer. Now I'm hunting around a proper interstage, I wish Lundahl has something for me. Don't you think it works?
With all respect for Mr.Kennedy DHT 26 circuit design !!! , but Man that`s way more complex for DIY than simple 6c45p ( or D3a ) tube SET driver circuit from Mr.Ciuffoly hybrid design !
Look only on that complex tube regulated PSU for that DHT 26 line amp , + you must there to provide extra grid bias circuit for 26 tube alone , it`s to much parts there Man ! ,just good to spend big money and to get trouble .
If you ask me my honest answer is : I will never start to build something like that to be the driver circuit for SS hybrid Circlotron power stage .
Actually I still think that Mr.Ciuffoly design is the right one , relative simplicity of driver stage unit + relative simplicity of SS Circlotron output power stage unit + relative simplicity of PSU = Relative Good Sounding Amp , Reliable and Easy to Maintain and to Modify .
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Enlightened Evolution-Astral Projection
Edits: 12/12/11
Yes, this is really true about the Amplifier End project is very simple and straightforward. I think all members here might agree the sonic character of DHT tube is very unique and unlike the others.
My friend has built a 26 line amplifier based on the KTA circuit and sounds wonderful!! If I build "only" the audio circuit of the KTA design, it's only has 1 tube as well. Since the KTA has tube regulation that made thing more complicated.
To be honest with you, up to this moment, I still consider which direction should I go. But no panic, since some of friend has started the project by building the Paul Hynes circuit with their own tube driver. I will see what the result is.
My first intention has considered circlotron with output transformer with 6C33C and has Tentlabs bias module with 300B for the driver stage. But I always think this is better to build a circlotron with MOSFET device and has DHT tube as front end.
One possible DIY way for you :
DIY Atmasphere M60 OTL Tube Amp !!! ,
On the DIY Audio site Mr.Ralph Karsten have Presented and full Supported International DIY community to DIY his Excellent Sounding M60 OTL Tube Power Amp .
Keith I strongly suggest you to read this full article !!! , there you can found so many useful information , schematics , dialog , advice .
Best Regards !
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Enlightened Evolution-Astral Projection
Hey! I decided to build the Amplifier End designed by Mr.Ciuffoly.
Smart Decision !
Since yours previous intention to DIY hybrid Amp based on combination of Mr.Kennedy 26 line amp + Mr.Hynes SS Circlotron well be Big jump in unknown .
BTW :
Great News for pure Tube OTL Circlotron Amp DIY people !!!
Mr.Ralph Karsten ( Atmasphere ) offers again DIY kit for famous M60 OTL Amp !!!
Best Regards !
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Enlightened Evolution-Astral Projection
I'm no interest to build a OTL with tube anymore. My friend has tons of OTL amplifier at home back in 90s such as you name it Atmasphere model with many tubes, Counterpoint SA-4 and Graaf from Italy, NYAL etc.
When those OTL play with loudspeaker which has high impedance, WOW, sounds is wonderful!! I guess the speakers we listened has Tannoy coaxial driver on it. Nothing can touch it!! However, it is not practical to "our" speakers with 8ohm load.
One of the most respectable OTL desginer Glenn Croft has designed many many OTL amplifier in UK. Around a decade ago, switch to solid state device right at the output and having tube for the driver. And cost a fortune, and the model name I guess is called Twinstar. It might be a marketing failure but I have consulted some of my best friends who are engineer why Glenn Croft is so stupid putting some solid state device and made a "hybrid" amplifier. they told me that Glenn Croft is smart since OTL actually act like a solid state amplifier in certain aspect, and the output stage is a buffer, the driver stage is the most critical part......
One of my friend is building Mr.Ciuffoly design's Amplifier End with E288CC (half the tube), and I will listened to that and made up a decision whether Paul Hynes output stage with KTA or Mr.Ciuffoly design Amplifier End is the way to go. I will choose between the 2. If my friend ends up a pretty good result, I will mod Mr.Ciuffoly circuit and accommodate a DHT tube there, since my friend says this is possible.
I loves OTL, but don't like the way they behave on speakers with 8 ohm or lower load, and I don't want to take any risk. If not, Counterpoint SA-4 driving a pair of LS3/5A (15 ohm version) in fellow system that I have come across is one of the most memorable audio experience in my life!!
But I'm getting greedy, I want the benefit of OTL but without the risk, so I choose MOSFET circlotron like Paul Hynes and Mr.Ciuffoly do. But I also want the sound from DHT, that's why thinking about putting a DHT at the front......All audio guys are greedy for "sound"!!
But I'm getting greedy, I want the benefit of OTL but without the risk, so I choose MOSFET circlotron like Paul Hynes and Mr.Ciuffoly do. But I also want the sound from DHT, that's why thinking about putting a DHT at the front......All audio guys are greedy for "sound"!!
Truer words were never spoken....
An i get you pont about the tube OTLs
The one big deal on the Sand amps,Got to be a diff. outputs...there sound can be sweet... An drive a real world speaker...Pass Labs get clost as i have seen...sound wise...I got the Krell MDA300 diff output amps to sound vary sweet,it the floting output...get that ground out of the speakers...Sound of the sand get vary good.
goodluck on your trip..hoho
Ck this out vary cool OTLs
http://www.tubecad.com/2011/10/blog0215.htm
So the grid stop resistor connected near as possible to tube socket is mandatory , and some small value 100Pf/1KV capacitor connected in parallel with driver transf. primary coil is good to for prevention of oscillation in RF range .
Great grid stop,info for anyone Diying tube amps,preamps any tube...
Thanks for the post
You wrote: "Mr Paul Hynes SS Fet Circlotron circuit is basically correct , but need bias circuit for output Fets which is not present on schematic from your link ! , it could be driven with small SET for sure , but I think that tubes 45 / 2a3 / 300 b is not appropriate for this application since the power MosFet devices usually need only few Miliwat for full gate charge/disharge control."
The bias circuit is not an issue since my friend can take care of it. However, for few milliwatt, I guess a step up transformer is more appropriate than any tubes, right? However, we still need gain from the driver, is it?
Anyonbe can think of any small DHT tube that will work in Paul Hyness circlotron output circuit assume we have a step down phase splitting interstage transformer between the circlotron output section and the DHT driver?
Thanks for the info!
You need Step Down interstage trans. for sure , not any Step Up trans. ! ,since the lateral power Fet`s works with max.AC voltage gate sving around 12-14 V , so the step down trans. have to be in range from 1:4+4 to 1:10+10 , that step down conversion ratio directly depends from chosen input/driver SET tube & SET Amp/driver configuration .
So any enough linear DHT triode which can produce around 1 W of output can easy drive up to 5 pair of lateral MosFet`s conected in Circlotron power bridge .
BTW , the quality of this small interstage trans. have Crucial impact to final Amp sound .
Best Regards !
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Enlightened Evolution-Astral Projection
Oh! When you say step down, it should be 10+10:1 and 4+4:1 not the opposte, right?
Sorry Keith !
I made unintentional mistake when I declare driver step down trans. ratio with signed range from 1:4+4 to 1:10+10 , that`s Wrong !
Right transf. ratio value should be from 4:1+1 to 10:1+1 !
Again : this driver trans. step down ratio depends from used tube type in SET driver unit and type of the power Fet`s for output Circlotron power bridge .
What`s important is to keep transf. secondary (1+1) DC resistance value at lowest level as possible , this value have direct influence on the final stability of the SS Fet Circlotron power stage ,`` speed`` of the whole Amp depends directly from this secondary coil DC resistance to .
Sorry again !
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Enlightened Evolution-Astral Projection
Edits: 12/10/11
Hey! come on! No need to apologize! You are helping me now!! So take it easy! I should say thank you to you.
The reason I want to clarify about the ratio issue since I don't want to present a improper info while placing an order for the transformer, and that's it.
Thanks again!
My friend will send me a DHT tube (not sure the type number) with plate voltage 130V, plate current 8ma with 5.5K plate resistance and mu of 8, will it work?
Also, can I put one of this specific DHT tube in the driver stage to drive "only one pair" of lateral MosFet connected in Circlotron power bridge?
Thanks!
It is hard to give you any precise reply since this small DHT tube type is unknown !
But for now Russian 6c45p military grade small triode with pure titanium plate work fine , D3a tube from Siemens triode strapped is OK to , but EL84 ( 6bq5 )triode strapped is very good performer to drive the 2 or even more pairs of power Fet`s connected in Circlotron power bridge .
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Enlightened Evolution-Astral Projection
The output device is a pair of IXTH20N50D, and it is a 500V 20A device. How much "max" power it can kicks out from CIRC1 when biasing high bias Class A/B or pure class A?
no text
Right !
If we assume that SS power Circlotron stage associated small SET driver Amp need unbalanced input signal voltage around of 2V which coming from PreAmp / or CD , or any other digital source , or similar .
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Enlightened Evolution-Astral Projection
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