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I've built a few battery eliminators, using an LM317 adjustable voltage regulator for the filament supply. You can use Zener diodes for B+ regulation; but, the B+ voltage is not nearly as critical as the filament. For a transformer, you can either wire two low voltage transformers back-to-back and take the filament supply off of where the two transformers connect or you can purchase a single transformer with the necessary HV winding.
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