Many design tricks were used to reduce production costs of the five-tube radio. The heaters of all the vacuum tubes had to be rated to use the same current, so they could be operated in series from line voltage. The rectifier and audio output tube required more heater power, so dropped a larger voltage than the other tubes. In many designs the rectifier tube had a tap on the heater to power a dial light. The plate current was routed through that portion of the rectifier heater, in order to make up for the current diverted to the dial lamp. If the dial lamp failed, that part of the rectifier heater would have a larger current which could burn out the tube in a few months. Early radios had a resistor network to minimize the problem but this was soon eliminated as the cost of replacing the tube was not the manufacturer's problem. As with Christmas tree lights, if one tube heater failed, none of the tube heaters would operate.