RE: Regulator for DLE 30 after the optical kill?
No, a 4.8 volt battery connects directly to the ignition box.
Most ignition systems should not get more then 6 Volts. Look at the label.
There are different diodes, most take .5 to .7 volts off.
A diode can be put before the switch, not a regulator as it will always draw some current when connected to a battery.
So typically your battery connects to the switch, then diode/regulator and then the ignition system.
For the radio circuit - a diode will likely not deliver enough current, mostly they can safely deliver no more 1 amp.
With a higher rate, they will heat up, eventually melt and shorten out (then they put out the full voltage) or disconnect (you loose power).
Most ignition systems take no more then .5 amps, Zenoah is at 2 amps, so you should be sure about this.
For powering a radio system - get a regulator. HK has them for less then $10, they work great.
And for high amp applications, a capacitor after the regulator is also a good idea to make sure you don't overload the electronics.