How much extra capacitance can I use?

[Axtman]

I am working on an Ampeg J-12 amp that has a 40/20/20uf @450v multi-section can capacitor. I am considering changing it to one I have in my stash that is 40/40/40uf @450v. Should I use it?

I know that transistor circuits require lots more power filter capacitance, especially in demand heavy circuits like bass amps. This is why transistor power supplies have hundreds or thousands of uf capacitance. I have been told that more capacitance on tube circuits can stress the rectifier tube, but the Ampeg amp has a solid state rectifier.

So back to my original question. When is too much capacitance too much?

[Justin Thomas]

It's generally only a concern if you have a tube rectifier, and then only for the first capacitor in the line. Which model if Jet & rectifier do you have? It may slightly change the tone of the earlier stages, but that's subjective.

Also, the specs on the vintage can were probably something like +80/-20% or vice versa. Meaning, it may not have been that far from what you have to begin with...

Jusyin

[Helmholtz]

I am working on an Ampeg J-12 amp that has a 40/20/20uf @450v multi-section can capacitor. I am considering changing it to one I have in my stash that is 40/40/40uf @450v. Should I use it?

I know that transistor circuits require lots more power filter capacitance, especially in demand heavy circuits like bass amps. This is why transistor power supplies have hundreds or thousands of uf capacitance. I have been told that more capacitance on tube circuits can stress the rectifier tube, but the Ampeg amp has a solid state rectifier.

So back to my original question. When is too much capacitance too much?

Regarding rectifier stress it's only the first/main filter capacitor that matters. And it seems that would not change using your replacement.
A general design analysis would mean evaluation of turn-on surge current and repetitive charging currents wrt. rectifier specs.

[Axtman]

Thanks Justin!

I have the Ampeg J-12.

[Justin Thomas]

Cool, you have a SS rectifier. The reason I ascked was cuz there was the first J-12 I think in the 50s, then the J-12-A, B, D, & I believe D. I've gotva T with the extinct & unobtainium 6BK11s, subbed w. 6C10s (also nearly extinct & unobtainium.

Justin

[g1]

As far as transistor amps needing more capacitance, I think it's more that the high capacitance values are not available at the high voltage ratings needed for tube amps. At least not affordable ones.
Even more so back when tubes were the norm for all electronics.

[Helmholtz]

As far as transistor amps needing more capacitance, I think it's more that the high capacitance values are not available at the high voltage ratings needed for tube amps.

Smoothing quality (low ripple voltage) not only depends on filter capacitance but also on charging series resistance and and discharging current.
SS amps generally are low impedance/higher current circuits. So for same smoothing they require much more filter capacitance than tube amps.