K&K Audio / Lundahl Transformers

RE: CCS for PP tube amp - self biasing?

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Radu,

You can certainly do this and it does improve the sound significantly in my experience. You simply return the grid leak resistor to ground rather than the negative bias voltage, remove the 10 ohm resistor and replace it with a pair of current sources (on heat sinks) adjusted for the bias current of your choice. The heat sinks for each channel need to be pretty large, with a thermal resistance of about 3 degrees C per watt or less. I have used the Aavid Thermalloy 530002B02500 for a pair of EL34s run at 50mA each with two DN2540 current sources sharing the load successfully, but you will need larger if you want to run more current.

The downside to doing this is that you will lose some power output due to consuming about 50vDC in the current sources for bias. It's not a big deal and doesn't affect the sound in a way that even comes close to nullifying the advantage of using the common current source in the cathodes.

Kevin Carter
K&K Audio
www.kandkaudio.com

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