05-30-2014, 12:23 AM
One problem though, none of those designs supplies the 135 vdc you need. You don't really need Zener diodes in a B+ supply anyhow, those battery eliminators from the 1940s and 50s used a Pi filter like an AC/DC set and there was minimal hum or ripple with the right size electrolytics. If you used a filter choke, or a solid state substitute, there would be no ripple.
I have a schematic someplace from a Radio Craft magazine that uses an old style circuit where they supply the bias voltages through a resistor network in the B- through a resistor network. I may have it on file someplace as I sent it to Bob for his Philco 623 project. These days you can hook up diodes backwards to achieve the same result off of a cheap transformer.
Regards
Arran
I have a schematic someplace from a Radio Craft magazine that uses an old style circuit where they supply the bias voltages through a resistor network in the B- through a resistor network. I may have it on file someplace as I sent it to Bob for his Philco 623 project. These days you can hook up diodes backwards to achieve the same result off of a cheap transformer.
Regards
Arran
