The Last Bass Outpost

Hello guys! My first post!

My Ampeg B-25B from the Magnavox era needs some service. Do you think a multican type cap is good? Like this:
http://en.uraltone.com/electronic-components/capacitors/electrolytics/jj-40uf-20uf-20uf-20uf-500v.html
Or would it be better to use modern discreet caps?

The rectifier has diodes right now instead of the tube. The rectifier tube sags nastily when playing bass. The problem with the diodes is that the voltages get crazy high. Right now the B+ is something like 550 volts. When the amp was made the line voltage was 220V, nowadays it's 235V. I've heard that the voltage could be lowered with zener diodes. Is that a viable option or shoud I give up and put the rectifier tube back in?