Thanks for the answer! Finally I got another 24mm Takumar and Tamron 80-250, both for $50!
I was reading about the yellow tint on the Takumar 50mm and I want to share my experience.
Reading somewhere (don't remember where) somebody says that using a LED light from IKEA got good results to remove the yellow tint from the lens.
I decided to try with a lantern from Nitecore, it has a high power LED
MH20GT
After 24 hours (and patience to recharge the flashlight every 2 or 3 hours) the change was great! Removed almost 90% of the yellow tint form the lens.
It's supposed that LED light don't emite UV light... but anyways it works.
Somebody know how it's possible?