Ampeg B-25B caps and voltages

[cowbellster]

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?

[amptech]

Welcome!

First, are you performing service yourself? If so, I suppose you are aware of  high voltage and that you are capable of working on such apparatuses...

You can use electrolytic caps of tha same value and same or higher voltage as the schematics say. Some like to use large MPL caps, and you can, but my tip is to stick with whatever that is closest to the original design.

As for the rectifier/higher voltage, if you have too high b+ with semiconductor diodes, you either have to arrange the filter caps so that they can handle the voltage or switch back to the tube rectifier. However, if your amp does not have a 240 volts input option, you are in troble anyway. It is a common problem, where I live we have 240V and some have 260. Check your heater supply, you need to have around 6,3VAC for the tubes to function properly/wear naturally.

There are numbers of solutions. I am sure the experts here will chime in, who have more time on their backs than me. What I like to do, is to use a bucking transformer. Some use resistors etc (or diodes, as yo say?) but I do not recommend it. Of course, you can use a 240 to 220 volts transformer, but it would need to be quite large. If you use a bucking transformer at 240-20 volts, you can get away with a much smaller transformer. 

[cowbellster]

I promise I won't kill myself with the amp! 

I checked the line voltage thing from the sticker behind the amp. I was wrong about it. It is made for 240 volts. Maybe the next thing would be to check the heater voltage.

[amptech]

If your amp is a 240V model and you got 235V in your socket, you'll be fine.

Unless you can arrange your filter to handle the higher voltage from your semiconductor diode mod, swap back to tube rectifier.

And if the sag still bothers you after new caps are installed, you have an excuse to buy another amp!