Filtercaps

[kniqht152]

Hey guys I got a question hopefully some of you experienced individuals can help me out.

I'm trying to recap an old fender bassman 100 and it's hard to find the exact same size (capacitance) filter caps to replace them with. Does it really matter if they are exact or can they just be in the ballpark, for instance a 100uf instead of an 80uf.

Also I've been browsing online and I've read about people doubling, tripling, or even quadrupling the capacitance of their filter caps in order to "tighten up" the bass response, how safe is it to do that sorta thing? Can I bust something by adding too much capacitance/filtering?

Thanks.

[Enzo]

It was vey common back then for electrolytic caps to have a toleranhce of +80/-20%. The actual capacitance could be all over the map. A 100uf cap with that tolerance could measure anywhere from 80uf to 180uf and be within the specs. It was not critical, and still isn;t.

If you are looking at the 80uf 75v filter cap on the bias supply, yes that will be hard to find. 80uf is a non standard value. 100uf will be fine. Not only that, but 75v is an odd voltage rating. SO look higher, like 100v. 100uf at 100v is my go-to filter cap for bias supplies like this one.

As to going larger, that bias cap probably doesn;t need to get larger by much. WOn;t hurt it if it does, but not needed. There is no current draw off that supply, so the voltage won't sag. No tightening occurs.

The main B+ (high voltage) supply has the pair of 100uf 350v caps in series as the first filter stage, that results in 50uf of filtration. You can make that larger if you want, make them 200uf or 220uf. The main concern over enlarging the filter caps is when you have a tube rectifier. Tube rectifiers have a maximum recommended filter capacitance to prevent excess current surges. But your rectifiers are solid state diodes, and they don't care. As to tightening up the bass, well, my personal philosophy is to make the amp work 100% first, then go back and make changes. You may find that nice fresh caps in the stock value make the amp play just fine. And it is one thing to say larger caps will tighten up the bottom end, but one really ought to consider just how loose the bottom end is before that operation. Sorta like a face-lift. A face-lift might make you look younger, but if you don;t look old to start with, then why bother?

[kniqht152]

Thats exactly what I needed to hear, thank you for that.