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Old 14th April 2012, 04:36 PM   #11
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Pauldune,

in Morgan Jones, Valve Amplifiers, 3rd edition, p. 136 we find Fig. 2.49 which actually corresponds to your topology #2. Never got it working, though using a stiff CCS as tail and two less stiff CCS's as plate loads, same as in Jones's circuitry. I strongly do believe that no one ever will go with it. Determining each plate current plus determining the sum of both will never work unless we use components with zero tolerances, including both triodes.

Best regards!
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Old 14th April 2012, 04:56 PM   #12
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Hey Kay,

Thats why I set both anode ccs's for MORE than 50%, and bleed of the excess current, and use that current to set the anode voltage. Or at least thats the idea. Hope to test it tomorrow; i have a pcb ready for schematic 1 that I can use as a base of experimentations.
(is that good english?)
I will try all topologies, and measure distortion psrr and so on... Then I will post it here.
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Last edited by pauldune; 14th April 2012 at 05:02 PM.
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Old 14th April 2012, 06:26 PM   #13
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And here is pcb v1 already...

Now I have to work on the powersupplies and some ccs pcb's
I hope to do some testing tomorrow....
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Old 14th April 2012, 06:46 PM   #14
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I just realised a that I could re-use a older powersupply; it even has 2 adjustable ccs's integrated... Changed the caps from 350 to 450v and ready...
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Old 15th April 2012, 10:19 AM   #15
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Quote:
Originally Posted by pauldune View Post
Hey Kay,

Thats why I set both anode ccs's for MORE than 50%, and bleed of the excess current, and use that current to set the anode voltage. Or at least thats the idea. Hope to test it tomorrow; i have a pcb ready for schematic 1 that I can use as a base of experimentations.
(is that good english?)
I will try all topologies, and measure distortion psrr and so on... Then I will post it here.
At least I do understand you ;-)!

Regardless whether you set the anode CCS's for more or less than 50% of the total current and bleed the excess by resistors paralleled either to the triodes or the anode CCS's respectively, this does mean that you reduce the CCS's impedance more or less dramatically - and at the same time their necessity.

Best regards!
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Old 15th April 2012, 01:20 PM   #16
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Yes, but....

I just measured schematic 1 and 3, and the difference in PSRR is dramatic.

The psrr without ccs in the anode line is zero (0); output ripple was the same as power supply ripple. (about 500mV pp)

with one ccs directly below V+ and a bleeder of 110kohm (like schematic 3) , I measured output ripple about 20mV.

I made one mistake on my pcb; 10K 1/4 watt resistor with 20mA current= smoke! (4watt dissipation)
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Old 15th April 2012, 03:32 PM   #17
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OK, schematic 3 isn't stable. (the one with 3 ccs's) It oscillates at 50 khz.
At least that's wat I think it is. It is a dirty sinus of 50khz, 100mV pp, even with shorted inputs.
The best now looks to be schematic 2; 1 ccs on top, 1 in tail.
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Old 15th April 2012, 03:38 PM   #18
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Strange thing, it is DC stable; 160v on anode's, 36mA through tail, 18mA through anode's. Voltage doesnt drift either...
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Old 15th April 2012, 04:12 PM   #19
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Quote:
Originally Posted by Kay Pirinha View Post
At least I do understand you ;-)!

Regardless whether you set the anode CCS's for more or less than 50% of the total current and bleed the excess by resistors paralleled either to the triodes or the anode CCS's respectively, this does mean that you reduce the CCS's impedance more or less dramatically - and at the same time their necessity.

Best regards!
It's a bad idea to use CCS's in the anode line and then NOT use some form of feedback to set the anode voltage. As you guys probably found, that's almost impossible to predict!
With some form of feedback to set Va they work great but open loop you keep on tweaking and then will find that they still run away with aging, temp and tolerances.
Some things are not meant to be

jan
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Old 15th April 2012, 04:34 PM   #20
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OK one step further! The 50Khz isnt oscillation!
I switched back to the other two schematics, only to find the exact same rubbish.
So I removed the testleads of the multimeter, only to find they were picking up the 50kHz.
I then went back to the 3 CCS version, and it works OK now! I had some 50Hz with strange spikes on the output, but it was the heater; I still run it with AC, and hadn't connect it to ground. Now I centered it around GND with 2x 1Kohm resistors, and the hum is almost gone.

I will try a DC heater soon.

I have to measure the distortion some other time....i've had enough for now

@Jan: Isnt the bleeder resistor a kind of stabilizer? The current through it keeps it at a constant voltage... Also it looks stable to me, after 1 hour of running the voltages measured are within 5 volts of the value I set them, and I dont see any changes anymore.
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