K&K Audio / Lundahl Transformers

RE: St-70 Premium Kit

129.242.34.67

In Reply to: RE: St-70 Premium Kit posted by KevinC on September 24, 2009 at 05:24:43

Thanks Kevin. This made me understand a lot more.
My concern is that if you bias up an output tube with a CCS "under" the cathode and the cathode then is lifted to a positive voltage while the grid is grounded, then there is a voltage potential across the CCS. The CCS needs this to work properly, and there is for a specific CCS a minimum voltage reqiurement for proper functionality. If you lower B+ and increase current thru the tube then this voltage drops toward zero, and the CCS might fall out of "regulation" - right? For a EL34 tube what is normally understood as "class A" operation is like 250Va/100mA, and the cathode voltage would be like up 12-13V relative to a grounded grid, and that is not sufficient for any kind of CCS.
I understand now better how the kit works, it was just the "class A" consept that confused me when I started thinking about how the tube output stage worked. "Forced class A" it is no matter how you bias the tube, as I understand now. Thanks again.

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RE: St-70 Premium Kit - KevinC 11:50:34 09/24/09 (0)

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