Tubes - KT 90 type 2 v.s. type 3

I'm trying to figure out if my KT-90 tubes are type 2 or 3. I've been told that there might be a difference in the number of welds used, but I'm not even sure where I should look for these (complete tube novice). Anyone know an easy way to identify these tubes? Thanks.
The type 2 will have weld spots all over the plates looking like a case of a measles. The type 3 will have folded edges on the plates, and weld spots goimng straight up and down ONLY where the plates are joined together.