Here is a very nice build from Dan Kercher on his contraption of the 300B amplifier with auto bias. The driver is an EF86 with SiC diode biasing, the topology is a hybrid mu-follower and a source follower drives the output stage. Filaments are DC with Rod Coleman’s board:
More details can be found below:
Hi Ale, I wanted to thank you for all of your PCBs. I just finished a project that uses your Gyrators, SiC bias boards, and SiC Source Followers. I'm so happy with the results. Details posted on Audio Asylum. https://www.audioasylum.com/forums/tubediy/messages/27/276814.html Cheers, Dan