[morzh]

The answers to your questions are:

1. Yes you can use electrolytic cap. I even think it was in the beginning as in those times I doubt a reasonable size 10uF non-electrolytic cap existed. It might but......so, yes, electrolytic is fine and it could be a Generap Purpose one, does not have to be anythings special.
2. The polarity is determined very simply: here's the rule, I am gonna write in in big bold letters:

IN EVERY SCHEMATIC THE NEGATIVE POINT OF THE RECTIFIER (TRANSFORMER CENTERTAP) IS THE MOST NEGATIVE POINT.

This means that the GND is positive relative to it, therefore the positive of a cap will go to it, if it is wired between GND and the centertap of the power transformer output winding.


Oh.....and there is nothing wrong with using film caps either. Then you do not have to think about polarity.

Another point:

The very first cap of the rectifier (right after the rectifier tube) should be a "high ripple" or "low ESR" (I prefer high ripple, though it usually means Low ESR and vice versa) type. The rest could be GP.