Welcome! Need support, you got it. Or share youe ideas and experiences.
Return to K&K Audio / Lundahl Transformers
99.178.170.55
In Reply to: RE: CCS with Cathode Resistor in a long tail ? posted by multiblitz on September 19, 2016 at 12:17:39
If you wanted to use plate load CCSs and a common cathode CCS (connected to a negative voltage PS), one or the other of the current sources will not be serving as a current source as they can't be set so that the plate and cathode current values are exactly equal. If place a 100K resistor from the plate of each tube to ground, then the current through the input stage is the sum of those through the tubes and those through the resistors, but the current through the common cathode CCS is only the sum of the tube currents. You can then adjust the plate current sources so that the current through the 100K resistors sets the plate voltages. To make this clear I will have to devise a schematic with the details. It may not come soon, but I will try.
Kevin Carter
K&K Audio
www.kandkaudio.com
Follow Ups:
Hi,
...a schematic would be really helpful...
Just to take my specific case: I want to rund a diff. pair as phase-splitter and driver for a p-p El34/Kt120. This tube will be the 6N6p. As discussed, I would like to run it with 20-24ma per triode. Normally, It would have an Anode-Voltage of 390V, an Anode-Resistor of 10K. Currently your ccs is on the cathodes which are tied together for bothh system as diff. pair. Grid is grounded with a 47k resistor.
I am not sire where you would put the 100k resistor in your example ?
Best Regards
Frank
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).
Replied to your e-mail with a schematic file....
Kevin Carter
K&K Audio
www.kandkaudio.com
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: