Thanks for all the answers. I tried measuring the light and I get a one stop
difference between the corners and the center. I will try to make a grade 5
print without any film and see what I get.

Matt, thanks for the tip. I found that the Lucky 90m looks exactly the same as
the Vivitar E-74 the only difference is the name and the color (Vivitar is
painted white and my Lucky is painted gray).

I cannot find the manual of either Vivitar E-74 or Lucky 90m but from a google
search the lamp recommended to the E-74 is the PH211. I try to get one and do
some tests.

Thanks again.