You need high frequency ac, the reason for high frequency is to establish and maintain the arc which is impossible wihout the hf.
Argon is the correct gas to use, as far as 4043 filler rod, it depends on the material you're welding. If I had to suggest a rod for 'general' purpose, that'd be the one I'd pick.
Mike

Hi jminn-Agree with Mike on the rod;- note also that you can
use an argon/helium mix shielding gas-generates a hotter arc and if you have adjustable wave shapes you can opt for better cleaning and less penetration or vice versa.
www.lincolnelectric.com have some great tips on their site.
Hope u get good results-TWWeld.

The GTAW process is used for welding the thinner sections of alloys.  Alternating current is recommended for general-purpose work since it provides the half-cycle of cleaning action. AC welding, usually with high frequency, is widely used with manual and automatic applications.  Procedures should be followed closely and special attention should be given to the type of tungsten electrode, size of welding nozzle, gas type and gas flow rates.   The preferred electrodes are thoriated, ceriated or lanthanated tungsten as specified in AWS A5.12 .  The advantage of these electrodes is that they have a more stable arc and can be used with higher currents that pure tungsten electrodes.  Agree with comments above on gasses.  The rod 4043 rod is very ductile but a little low on strenght, what alloy are you welding?

Stay with pure tungsten for alu.

Been welding aluminum for years......use pure tungsten ..........obviously someone has been reading a little to much....2% thoriated will last longer but is generally used for stainless.....and when you grind it wear protective gear because it is radioactive.......the choices you have made are good ones