You could burn them dry if you keep the temperature on them under the tungsten boiling point at the desired vacuum, i always do like this and have never accidentally deposit tungsten if they happen to run dry.
The only thing to check is so that the energy in the aluminum vapor isnt to low so it wont stick and i havent checked this into detail yet but the boiling point for tungsten is much higher then for aluminum so based on this so shouldnt it really be a problem as i see it.
I have an homebuilt 1000A transformer to the tungsten and yes it could be quite easy to put to much power in bigger coils and especially in smaller but you have to check the amperage all the time so you know that it is the same power every time in the coils so they wont get to hot.
Regards Henry
