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 Post subject: ccs bias question
PostPosted: 21 Oct 2017, 04:35 
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Joined: 27 Nov 2016, 07:15
Posts: 11
Location: Holland
I'm looking at the vta st70 schematic. It uses a ccs (sink) in the second stage that sets the current to 4.2mA per tube half.
I don't see any voltage drop resistor. Does the constant current through a tube and the 0 volt grid force the kathode to a destined voltage level? Can it work that way?


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 Post subject: Re: ccs bias question
PostPosted: 21 Oct 2017, 05:07 
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Joined: 29 Oct 2014, 12:32
Posts: 95
Location: Russia Komi republic
Well... Why you need cathode resistor? To set current per tube ( some volts drop on this resistor, so this voltage with minus will be on grid, so it's you bias). Bias and anode voltage set current. It's auto bias. When you anode voltage rise, more voltage drop on cathode resistor, so you go to next bias point.
When you have ccs, you ccs set current.

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 Post subject: Re: ccs bias question
PostPosted: 21 Oct 2017, 05:12 
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Joined: 29 Oct 2014, 12:32
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Location: Russia Komi republic
I described the situation as a whole for a triode, for example. in the evening at home I'll look at the scheme that you are talking about. I can answer for sure

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 Post subject: Re: ccs bias question
PostPosted: 21 Oct 2017, 06:06 
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Joined: 27 Nov 2016, 07:15
Posts: 11
Location: Holland
okay, cool. I know how to bias a tube, and voltage drop and such. But i can't figure out how the positive voltage on the cathode is exactly established in this circuit


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 Post subject: Re: ccs bias question
PostPosted: 22 Oct 2017, 03:37 
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Joined: 01 Jun 2013, 09:05
Posts: 601
Is this it?

http://www.usaudiomart.com/details/6490 ... es/587629/

Yes the splitter uses a CCS current sink.
No it doesn't need a Cathode resistor because the CCS sets the current through the tube.
Ie the CCS is working in place of the cathode resistor. R27 10 ohm sets the current through the regulator.

You can do a similar thing with diodes, LED's etc.
LED bias, or diode bias. Or in this case CCS.

You can also use a Mosfet amplified zener as well.
You can use a discreet circuit for CCS as well. :P
Its how long is a piece of string or in this case how many ways can I play with a circuit.
Then there is the belief systems about bipolar transistor bias as opposed to Mosfet etc.
NB this is not unusual just different.

Regards
M. Gregg

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 Post subject: Re: ccs bias question
PostPosted: 22 Oct 2017, 03:50 
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Joined: 01 Jun 2013, 09:05
Posts: 601
Just for interest,

The baby huey amplifier used the same idea with discreet CCS.
Link:
https://www.google.co.uk/search?q=baby+ ... SEyLPGKjzM:

So there you go. Pretty much standard with "new" tube circuits. (Sand in glass) :eek: :D
You mean all the diodes are glass passivated<<er no..LOL

Regards
M. Gregg

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 Post subject: Re: ccs bias question
PostPosted: 22 Oct 2017, 03:59 
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Joined: 01 Jun 2013, 09:05
Posts: 601
If you like tech info,

http://valvewizard.co.uk/ccs.html

Not much else to say...or is there? spooky.. :alien:
Enter the twilight zone:
https://www.youtube.com/watch?v=-b5aW08ivHU
The vertigo record label comes to mind.


Regards
M. Gregg

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 Post subject: Re: ccs bias question
PostPosted: 22 Oct 2017, 04:51 
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Joined: 27 Nov 2016, 07:15
Posts: 11
Location: Holland
sorry for the long wait. i was drunk. :)

Do you mean to say that because the ccs sets the current that the tube kathode is forced to a voltage?
you know what i mean?
normally you would set the bias to force a certain current. But with this ccs you set a certain current to force the bias?

and yes that is the schematic that I meant. I have that exact same thing at home, bought it from tubes4hifi. It sounds extremely good. But now I am a tube addict!! :(
And trying to build my own little tube amps! lots of fun!


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 Post subject: Re: ccs bias question
PostPosted: 22 Oct 2017, 04:58 
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Joined: 27 Nov 2016, 07:15
Posts: 11
Location: Holland
:) and yes, I know the valvewizzard. learned a lot on that site. also leanardaudio and aikenamps and a couple of more sites.
But even when building your own amplifier... SO EXPENSIVE!!! :)


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 Post subject: Re: ccs bias question
PostPosted: 22 Oct 2017, 05:41 
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Joined: 27 Nov 2016, 07:15
Posts: 11
Location: Holland
and i looked at the baby Huey again... but doesn't it use the 2 470 ohm (and the 1k balance) kathode resistors to up the voltage on the kathodes?

The st70 doesn't have that. That is why i don't understand it.


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