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RE: BDT Preamp Schematics

Posted by kenev on May 13, 2008 at 09:45:53:
Hi John,

Just another of your excellent "weird" designs (actually an improved version of your previous BDT preamp). Glad to see the new, revised circuit. I had purchased a bunch of 6AR8 tubes a couple of years ago, when I first saw your BDT preamp, but never sat down to work on it. I think now is the time for it, although this version is a bit more complicated than the previous one.

Just a couple of questions:
What is the bias voltage for the cascode? (I suppose that trimmer R13 is for setting the bias voltage). Also, do the IRF820s of the cascode circuit need any heatsinking?

Regarding the OPT, what is the primary impedance? As I have built a DIY winding machine and I wind my transformers myself, do you think that Dave Slagle could give me some more information regarding the design of this OPT?

Regards,
Evangelos