Dumb question about electrolytic capacitors

[zhyla]

So I'm wiring up this bassman amp (schematic attached) I've been working on and realized that I ordered electrolytic caps for the 25 uF caps. Clearly they will be exposed to AC signal. Now I know electrolytics are polarized. Will they explode? It seems even the ones that have ground on one side may experience negative voltages relative to ground.

I'm pretty sure I used electrolytics in this manner on my first amp and also a guitar pedal but that doesn't mean it's right and won't bite me in the rear. Should I order some non-polarized caps for this instead?

Edit: I just found out why I chose electrolytic for these caps. Mouser didn't have any other 25 uF options except some $25/each film caps. Yikes!

[tubeswell]

Perfectly normal to use electrolytics for cap bypass and filter caps - its what everybody does. The reason that most 25uF are electrolytics is that they are small enough to fit in your amp comfortably and they are easier to come by. That rating in a film cap would be physically quite a bit larger.

For cathode bypass or filter cap applications the -ve end goes to ground.

For bias supply decouplers, its the other way around, the positive end goes to ground

[Enzo]

There may be an AC signal involved, but the voltage across those cathode bypass caps is not likely to reverse in polarity. A signal that varies from +1v to +3v might be a 2vAC p-p, but it is still a positive voltage all the time.

Might be too late now, but for example C9-C12 are 16uf caps. That is an odd value today. It would be perfectly fine to use the very common 20uf or 22uf caps in their place.

Likewise at the input stage, there is a 250uf 6v cap. No reason to hunt one of those down, you can use a 250uf cap at 16, 25, 35, 50, whatever volts.

[zhyla]

I'm building this amp out of an old organ amp which already had some old-style cylindrical filter caps. Oddly they still seem useable after all these years - there's two 60 uF and one 30 uF, a little overkill but workable. I bought some 33 uF just in case, they were cheaper than the 20 uF's.

What is meant by "bias supply decouplers"? Can you point at one on that schematic?

Thanks for all the help guys.

[tubeswell]

The 5B6 doesn't have a bias supply, so it doesn't have bias supply caps. I was just mentioning it by way of example. In a 5G9 for example, there are two of them in a Pii RC filter for the bias supply.