If you go to Hitec's webpage and read the specs for their HV servos it states 7.4v and 6.0v input voltage for their HV servos . Running lower input voltage than 6.0v would work but the servo performance will be very weak and slow. I have several planes with HV servos and have been running them for quite a while. The HV model servos have similar performance specs to their equivalent standard voltage servos, not extra power from higher input voltage or different power source. It is still best to run a regulator to keep input voltage constant under load and flight to flight. This is very helpful for precision aerobatics etc.
There are two advantages to HV servos, weight savings of lipo cells and running higher input voltage to the Receiver. Higher input voltage for a 2.4 receiver helps prevent brown out situations that can happen with most any brand receiver. An ounce of prevention saves pounds of cure.
Originally Posted by liukku
The high voltage servos, such as Hitec's, do they work with 4.8V-6V voltage?