Hi! I need 15V regulated dual supply, and I've decided to go with Zeners instead of IC regulators. So I have two questions: - what would be the value for the resistors in series with the Zener diodes? - I'd also like to have switchable 7.5V dual supply; can I use some DPST switch which would switch on and off the 7.5 Zener diodes in parallel with the 15V ones, and also, what would be the resistor value for the 7.5 diodes? The transformer would be +-22V or +-18V. Thanks in advance!