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RE: Constant Current Source for Dynaco ST-35

If you do as the previous poster suggests and change to a "long tailed pair" phase splitter you could also replace the plate load resistors with a CT plate choke (Lundahl makes a good one). You would then set the reg. B+ to the plate voltage you want (plate chokes and transformers "pull down" from the voltage they are fed). I use this arrangement in my power amps (input stage CT plate choke loaded direct coupled to driver stage with IT). It works really well.

You could also use CCS plate loads instead of resistors. This would require adding resistors from the plates to ground (somewhere in the 20-30K range; pick a value that will give you the plate voltage you want with ~5-10mA). The excess current in the plate load is shunted across this resistor. Ohm's Law then gives you the plate voltage. Also calculate the heat dissipation and size accordingly. By adjusting the plate load CCS you can change the plate voltage. While adjusting the cathode current source you can set the bias (if you change the bias you will need to readjust the plate loads). This is a nice arrangement if you want to experiment with different operating points. The input stage of my phono pre uses this configuration. So does the input stage of Kevin Carter's ST-70 kit over on the K&K Audio forum. He also sells CCS kits which are very handy for this.


"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln


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  • RE: Constant Current Source for Dynaco ST-35 - JKT 12/12/1422:05:57 12/12/14 (0)

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