John, I never had a problem with my 60's De Vere cold cathode head and VC papers with below the lens filters. However the tubes can vary, I had to fit a new one and it was much better, the output was bluer. I've never needed to push to the extremes of a VC paper virtually all my negative print easily on Gd 2 or 3 so I never tried 00 or 5 and the usually criticism of Cold cathode heads is lack of those extremes.