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Help with CCS ?

Hey all.

I'm currently working on a tube phono stage. It has a single power supply, and 4 KandK CCS's, feeding current to four C3G pentodes (wired as triodes).

As part of the setup, I configured all four CCS's using a 9V battery, and a 10ohm resistor, and configured each of them for 18ma. This will give the tubes about 180V on the plate, and a bias of about 2.5V (there's a 130ohm resistor on the cathode)

Once powered up, three of the tubes show "correct" values (they bias at 2.3V, and have between 165 - 180V in the plate, which I put down to tube variation).

The last tube, however, is biasing at 3V, with 220V on the plate.
I tried different tubes, but the problem didn't follow the tube.
I removed the CCS, and tried testing it with a battery and resistor, and it measured fine.

Can't think of what else to check ?

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Topic - Help with CCS ? - MichaelM 05:19:57 06/06/12 (19)


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