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Old 17th February 2012, 10:04 PM   #1
kees52 is offline kees52  Netherlands
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Default 6AS7 hybride CCS

hi all.

I have need for a ccs where I can make use of the both sections of the 6AS7, because of its low mu it is not so good a ccs, but when I use solid state around it then I can maybe use it, I will be happy if someone has a nice idea, it is for dc coupling to mosfets power output hybride amp.

i wil try a platefollower as driver, now I have cathode follower, so see what is the sonic difference and also it is a very beefy driver for mosfet capacitances, it can have a sonic update.

on picture I have some examples.


thanks.

ScreenHunter_04 Feb. 17 23.56.gif

Last edited by kees52; 17th February 2012 at 10:07 PM.
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Old 18th February 2012, 10:05 AM   #2
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That tube needs a lot of grid-cathode voltage and will eat a lot of your available voltage for signal swing. Besides, it seems like a waste of power using two of these tubes for such a duty (16watts per tube for heater alone!).
Better to use a single tube and one triode section per channel, and transistor ccs on the plates.
My pennies anyways.
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Old 18th February 2012, 01:21 PM   #3
kees52 is offline kees52  Netherlands
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the idea was big drive for the mosfet capacitances, special when she are paralelled, there are people who run class a who eat 1000 watts, so what is 16 watts, I do the tubes in series, but like you say it is possible to use one in stereo channel.

I put heaters in series, no big deal.

the supply is bipolair 2x120 volts.

the transistor version hybride css is not stable, the depletion fet versie is very stable, I need to inject a correction signal for offset tracking, I don,t now well how I can do that with the mosfet version, maybe a 100k resistor in series with the 6AS7 tube and inject there, I need high impedance for it.

it is dc coupled to mosfet gates, so I need offset tracking with opamp.

thanks for reaction and have a nice weekend.
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Last edited by kees52; 18th February 2012 at 01:29 PM.
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Old 18th February 2012, 08:44 PM   #4
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I dont get half of your circuits...Why the 33ohm on the bottom? What voltage are the lower grids suposed to be at? Is this DC all the way or AC to the 6AS7? Your first schem has the grids of the top tube too high, will draw grid current if it works at all. 8ohms to set teh current? will that give 60mA? The second schem, well I know nothing about that MOSFET....The third, wont the N-MOS keep the voltage constant? Be like a voltage source and not a ccs?
Remember tubes have temp drifts as well...and the types of ccs u have in ur schem are not very temp stable. Perhaps you should look into more stable ccs? I don't think having a 6AS7 part of the ccs will solve that particular problem. Though the high grid-cathode voltage makes them suitable as cascode elements I guess.
What is the total input capacitance of the MOSFETs you are driving and how much voltage swing do u need? Doesn't matter how many amps you drive thru the driver, it's the driving impedance that sets the fc. I know u need enough current to slew the gates, but no need to over-over do it.
I don't mean to diss your idea, I like these tubes and they can be good drivers I guess, but I think u should look at where the drift is coming from.
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Old 19th February 2012, 01:20 PM   #5
kees52 is offline kees52  Netherlands
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Hi

That is why I post it, to trigger reactions, the one hybrid tube bjt (left) do not work well, I have seen, indeed because of grid voltage, the resistor 33 ohm is for get 0 volt on center, that is what I need if it is dc coupled, but as you now it is test and simulation, nothing serieus about now..

The left one with the mosfet is what I have use for two years in a amp, I have a working one you now, see pictures, the white follower is what now is in use, listen to the music in youtube link. 40 a 60 volts swing is enough, I use lateral mosfets 3 pairs each channel, A mosfet driver extra will also work fine I think, maybe that is a option, like I did with the hybride circlotron who uses only n-fets and is ready for the new j-powerfets.

You are right, tubes are not so stable in offset voltages, but here I use a offset tracking ic who also track the aging if the tubes.

I have read somewhere that a 6as7 driving mosfets in a dc way and powerfull, elastic effect is gone, the sound is far more romantic and fast, warm because this tube can easely go on low voltage and also deliver a lot of current.

Drift is what all tubes are doing, but that is not a problem, the ccs with the mosfet is very stable, don,t drift itselfs, the tube do.

There exists CCS hybrides who works with tube as power part, advances is that I dissipate power above the chassis, and so I make use of both parts of one tube, but I can also do use one, with a mosfet CCS on top, for stereo one tube, but crosstalk can occur.

By the way get grid voltage down is not difficult, because the cathode is on 0 volts that is needed for 0 volts offset of amp.

you don,t diss my ideas, you now I am a bad calculator, I try combine and simulate, calculating and such is not needed anymore for the most parts, it is fun simulating
and see what topologies do in multisim.

thanks for your reaction.

6C4N-EB hybride - YouTube
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Last edited by kees52; 19th February 2012 at 01:35 PM.
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Old 4th March 2012, 06:02 PM   #6
kees52 is offline kees52  Netherlands
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So to pump some live here, I have already learn for the solution, for me tubes are not so long used as I did use total solid state in the old days. but I love this way and she get my attention.

oke, the old pictures here are al bad, so I have deside to use a solution who is very nice for me.

see the pictures, it is a mustage for high power drive to the mosfets, and also now the first driver for me who amplifies 2.4 X so I did use a plate follower with a high current triode 6C19P and not the 6H13C who is quite non liniar in comparison with the 6C19P, a plate follower give me also the option to use far less voltage amplification what is needed if I did use cathode follower with this low mu tubes, and include current feedback if needed, now it is without feedback at al, even de platefollower has non, cathodefollower has 100 procent who made the sound clinic, so that is why I will test it this way...

Now I have a lot of drive to keep the mosfets follow the tube output strikt as what I want to prevent audio distortion the solid state way.

distortion measurement is with test build with only the mustage and tone generator 10 volt pp
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File Type: gif ScreenHunter_03 Mar. 04 20.02.gif (21.4 KB, 323 views)

Last edited by kees52; 4th March 2012 at 06:08 PM.
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Old 26th March 2012, 01:18 PM   #7
kees52 is offline kees52  Netherlands
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I don,t now yet but the mosfet 2sk1058 did blow, because if the tube is not warm yet 120 volts is present on the gates, but will this blow the fet, the aother one I have playing in home has minus 120 volts at the gate when cold tube, this is maybe the ddifferent that it is possible.

I have discover that the mosfet did oscillate very heavenly and blown there gate resistors, most of the time then the fet is broken.

I think and ask, can a oscillation (35 volts on output) blow the fet, wil it give his own gat e a high voltage and break it.

thanks.
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Old 31st July 2012, 07:05 AM   #8
dady is offline dady  Argentina
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Quote:
Originally Posted by kees52 View Post
hi all.

I have need for a ccs where I can make use of the both sections of the 6AS7, because of its low mu it is not so good a ccs, but when I use solid state around it then I can maybe use it, I will be happy if someone has a nice idea, it is for dc coupling to mosfets power output hybride amp.

i wil try a platefollower as driver, now I have cathode follower, so see what is the sonic difference and also it is a very beefy driver for mosfet capacitances, it can have a sonic update.

on picture I have some examples.


thanks.

Attachment 266809

Hi Kees, I never imagine that you are Hollander, I found you here in this post and thank again for your contribution.
I will try the diagram.
Best Regards
__________________
Esteban Bikic
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Old 31st July 2012, 10:24 AM   #9
kees52 is offline kees52  Netherlands
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Quote:
Originally Posted by dady View Post
Hi Kees, I never imagine that you are Hollander, I found you here in this post and thank again for your contribution.
I will try the diagram.
Best Regards
I did mail you, these old topic was before I did start the double mu stage amp.

I have not use the 6as7 but the 6c19 now.

Yes I from holland, here a a lot hollanders on diy, if you search you find more of me, I have somehow contaminate this forum, but now I try to stay on one place.
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