model 7405-1 4 tube 6d6,6c6,43,and 25z5.it says it needs resistance cord.can you tell me what i need ,to install a regular ac cord.

The 25Z5 and 43 tubes are both 25 volt 300 mA tubes. The other two tubes are 6 volts at 300 mA. Adding the voltages, you have 62 volts. If you want to run your set off normal 117 VAC, you will need to drop (117-62=55 volts). This can be done with a resistor in series with the heater string. The resistor value therefore would need to be 183 ohms (or something close, like 180 or 185 ohms) and it would require a current rating of about 25 watts (derated from 17 watts for reliability). This is a substantial resistor and will get warm during operation, so some thought will have to be given to its placement inside the set to avoid overheating/possible fire hazard.

You can install a dropper cap or resistor: http://www.vintage-radio.com/repair-restore-information/valve_dropper-calcs.html

A dropper resistor will put out quite a bit of heat, so a cap would be better.

Until it shorts!

OK, good point. But if the cap were to short, which for a properly ac-voltage-rated modern cap seems unlikely, it would open the fuse (if any), or one tube's heater would blow and open the circuit.

For me - I just want to get my old radios working, and then hardly ever play them, except as a demo. So, the heat from a dropping resistor wouldn't keep me awake at night. Go with either the cap or the resistor, and be happy.

Just for laughs, I calculated the size of capacitor needed to replace a 183 ohm dropping resistor: looks like the exact value is 14.5 uF at 60 Hz, but 14 uF would probably be close enough. This is a reasonable size for an electrolytic and would be inexpensive, but a nonpolarized cap would be needed, or two polarized caps connected in series, joined + to + with a bypass diode on each to avoid subjecting either one to reverse voltage on each half cycle.