Got a new idea and first planned to build a budget amp with a mains-toriod and a triode-strapped tetrode. But maybe one could build a "serious" amp on the concept instead.
The nice thing is that no current balancing is needed as both primarys are in series and opposite polarized. The downside is that B+ has to be higher. The simple CCS is made with a 500V P-channel MOSFET from OnSemi.
If using a PP transformer note that the CT must be opened up and one primary winding reversed.
EDIT: Remade the text and the overly complicated ciruit as noone answered last time. Some comments would be appreciated this time .
Concept should work reasonably. You can trade the high voltage relatively low current for lower voltage at 2x the current, and avoid needing to "turn around" the winding by placing the "current" device as a current sink in the "other half" of a push pull configuration. (The 6B4 on one side, a current sink on the other) to balance out the DC in the windings.
I've experimented with those power supply toroids... they're reasonable, but not nearly refined enough for critical listening. That is, they sound OK, but not GREAT. What they do offer is reasonably good frequency response, and they're relatively inexpensive.
Hi Stephie,
We actually began with the concept you described but with a tetrode instead of the MOSFET. Built it and showed the results at diyaudio a few years ago. Great success at the yearly Swedish DIY-fest.It is close to the schematic below, the only one I could find.
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