Grid choke

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Direct coupling allows to go into AB2 operating mode, driving the power tube grid into positive voltage against the cathode. You will get grid current and as a consequence a lower saturation voltage between anode and cathode. This leads to more clean power. In my case that mode has increased the clean output power from 300W to ~ 350W.

The second effect is that you will have a stable bias for the power tubes.

You can see here how I have implemented the direct coupling: Bass Power Amp with GU50 . It includes also a limitation of the maximum positive grid voltage to protect the grids.
 
I see high-voltage regulator kits of various kinds. I also see high-voltage grid bias supplies that monitor the cathode current. They react slowly, not to the signal, supposedly. Seems to me the grid choke is a good alternative, because it makes such a high impedance to the grid at audio frequencies. I kind of like that, and it should be a good thing with 6 output tubes in parallel. I will probaby start with changing from the stock half-wave diodes to a full-wave rectifier and bigger cap to just one choke, then a resistor and bias pot for each tube. If the choke causes it to lose bass, maybe I can just add a carefuly-tuned cap after the choke before I resort to multiple chokes.
 
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