The choke is a 1/2W choke. It's actual measured resistance is .45 ohms. Let's say I'd dissipate 1/4W to be safe, that's still .7 amps. I don't think the choke is a limiting factor. 
The regulator would be overheated long before you get to .7 amps unless it has a pretty substantial heatsink. With a 1/2 amp load, you need at about 1000uf filter cap to insure regulation with 18 volts input. If the input voltage was lower, you'd need more filter capacitance. With 1/2A output from the TO220 regulator, you also need a fairly hefty heatsink.
