SteveH

Thanks a lot for the info. I actually did read the above posts first, and still was confused. The "cam stack" comments did not clarify it originally.

Now i get it.

The reason I ask is that although i am planning to shift my "collection" to pre electric machines, these are cool enough to want to have and use at least one.

The 403's around here seem to go for about$100 whereas the 503's are about $250. Worth asking to clarify the differences.