2000uf 30vdc - ok for cathode bias bypass capacitor?

[yello]

I scored a box full of 2000 mfd 30 VDC capacitor cans at a swap meet. Assuming they test good, would they work as bypass capacitors for cathode bias on power tubes in an 18w? I think I typically see 50-63v as the spec on schematics, but assume that is high to be on the safe side.

If not an 18w, would they work in that function in any circuit?

Likely easier ways to get the right part, and maybe a smaller format, but the acquisition inspired the question.

[TriodeLuvr]

I wouldn't find those to be worthwhile for that use. For one thing, they're big, and they require special mounting compared to a simple axial capacitor. They're also likely to be old, and it's difficult to justify their use as opposed to buying new electrolytics. Digikey has 100uF/50V axials by Cornell Dubilier for $1.11 each in single quantity. They'll even ship for free if you mail a check with the order.

Jack

[Bieworm]

Jack has a point, but he didn’t really answer your question. Yes you can use them with EL84 tubes, NOT your 6AQ5 tubes.
Besides, there is no danger in having a bypass cap crap out as long as it doesn’t short. It only sounds horrible with the resistor only.

[yello]

Jack has a point, but he didn’t really answer your question. Yes you can use them with EL84 tubes, NOT your 6AQ5 tubes.
Besides, there is no danger in having a bypass cap crap out as long as it doesn’t short. It only sounds horrible with the resistor only.

What makes them useable for el84, but not 6aq5? The large value? On my military amp project it was suggested here on 18w.com (by zaphod_phil, and you) that I use a 1000uf or 2200uf and it is PP 6aq5's, and it worked and sounded fine.

Do large value cathode bypass caps on a bias resistor only work with el84's, not octals like 6v6, 6l6, el34, etc? I've only read about the 1000uf/2200uf values in the 18w context, but would love to learn more.

[Bieworm]

Look at the cathode voltage. The EL84 will be around 12V , but your 6AQ5 will be around 20 to 24V if I recall correctly.
Let me put it like this: never exceed 50% of the voltage value of the cap and you’ll probably be fine. And you normally won’t harm the amp if the cap blows

[yello]

Look at the cathode voltage. The EL84 will be around 12V , but your 6AQ5 will be around 20 to 24V if I recall correctly.
Let me put it like this: never exceed 50% of the voltage value of the cap and you’ll probably be fine. And you normally won’t harm the amp if the cap blows

Oh, did you mean don't use these 30v versions with 6aq5? Not never use a 1000uf/2200uf with 6aq5?

I don't necessarily plan to use these cap cans for the size and voltage limitations they present, asking more to explore and understand. They were free at the swap meet.

[Bieworm]

Oh, did you mean don't use these 30v versions with 6aq5? Not never use a 1000uf/2200uf with 6aq5?

As I said, your 6AQ5 tubes will be biased with a higher cathode voltage. When you would stay under 15V there would be no harm done with the 6AQ5. But the 6AQ5 is a substitute for a 6V6GT and will have a cathode voltage above 20V if you want them to sound good. That 20V or more will push the caps to their limit and a >50V cap would be advisable.
In general there is no reason why you wouldn't use higher spec'd caps, unless you have some lower values on hand like you do. You could try to use them with voltages above 20V, but the risk is on you. Remember, those caps won't blow right away if you stay under 30Vk, but they will probably crap out on you at a moment you are not expecting it in a less ideal situation like band practice or a gig. Murphy is always looking over your shoulder