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RE: CCS with Cathode Resistor in a long tail ?

Posted by multiblitz (A) on November 12, 2016 at 15:56:58

In Reply to: RE: CCS with Cathode Resistor in a long tail ? posted by multiblitz on November 11, 2016 at 21:03:43:

Or let me describe my thoughts and see if I understand it:

- I want the 6N6p to run at a Bias of 150V on the anode with 20 mA which requires -4,5V. currently my Load resistor is 10k, so with HV+ of350, it will drop the voltage from 350V to 150V and will produce heat of 0,02*200=4W each.

If I want now the same bias, the CCS needs to be set at 20mA. It would replace the Plate resistor with + goes HV and - goes Anode. Bias needs to be set by a resistor, normally to produce -4,5V this would mean R=4,5/0,02=225Ohm...as this resistor has two triodes to serve /diff pair), double current, so actually it should be 112 Ohm.

In the impasse-preamp the guy used LED to produce the negative voltage instead of a resistor...

Ok, back to the CCS. As we force with the negative grid voltage the operating voltage and with the ccs the current, the same 200V would drop over the CCS, correct ? So it would need to stand 4W.

If I now want to relief the CCS ( I am using the compact CCS with up to 2W), I could put a 5K resistor between the CCS and the Anode, so that 2W of the 4W in total will drop over that resistor and the other two over the CCS....correct ???

Any disadvantages ? Any wrong understanding ?

I found this setup as well here: http://www.audioxpress.com/article/The-ImPasse-Preamplifier ...R4 is the trick

Having this 5kresistor in place there will allow me to set the current as well...(still not sure how your 100k setup would work).

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