Toyota Repair: Repeated Alternator Failure, toyota corolla, voltage regulators

Question
Hello Ted,
I am having some kind of electrical problem with my 1987 Toyota Corolla.It's a carbureted,4 cyl,1.6L model.Automatic transmission. Milage:187,300.
A few days after I bought the car the alternator went out.I got a new one for it .But 2 weeks and 200 miles later the new one went out too.Since I had a lifetime warranty on the alternator I got a replacement.I had it put on.But the same evening my lights went dim,charge light still stays on and the new battery went dead.
I had the fuses checked near the battery;all are ok.The belt is tight but a little worn.
Have any ideas what could be causing these alternators go so quickly? What should I check for next?Thank you for assisting me.  

Answer
Make sure that the correct alternator is installed, some of the systems had external voltage regulators and some had an IC regulator built into the alternator, they are not exchangeable. If the alternator has an external voltage regulator replace it also.