MagneQuest/Peerless Forum

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UL tap on parellel feed?

Posted by Sector-7G on May 16, 2004 at 07:45:25:
HEY-Hey!!!,
The parafeed UL is an interesting proposition. SE and UL but with DC-Free primary L.
There are a few options, and depend on the plate load. An inductive plate load will need a larger B+ for the screen signal than a CCS type. The goal will be to provide a low output z screen supply, modulated at the UL tap's fraction of plate signal.
A cathode follower, or source follower will do an adequate job. Set up a seperate rail, at 2x B+, and self bias a cathode follower at what ever fraction of B+ you want the screens to operate at under idle. cap couple its grid ( or gate )to the U-L tap, and you're off to the races.
For a low voltage tube like an EL84, an IRF820 might be a reasonable choice, or a 12BY7 ( relax Eli, there won't be enough folks doing this to make them any scarcer for your Brown Monster ), or maybe a 5687...
regards,
Douglas