Choosing the right filter cap

[Mikante]

Hello,
I have a question, i m looking everywhere to find some info.
I have a small amp that i have modified so many times that the pcb is now a mess.
I swapping everything out for a point to point board, i might leave the rectifier part of the circuit, because i really like the punch and quick response. It is a fender champion 600 by the way.
I have every thing sorted out but i found my self lacking knowledge about filter caps and how to choose tham.
I mean, i know about the values, i need 20/25uf, 450v is the stock value but i read they can be swapped for smaller ones.
Here is where i find my self confused. Do they just need to be electrolytic cap and of course with proper values? I mean any electrolytic will do? I see there is a lot of difference between different types, some are very expensive and some not and this makes me feel like i missing something.
Is there a specific type of cap used to filter the power section? For a cap job as they say.
I need axial cap.

[pompeiisneaks]

That's a pretty complex question... I'll do my best to answer

Basically you need to get an exactly or higher voltage rating than the exising one. I.e. 450VDC it must be rated for that or higher, say 600VDC or the like.

As for capacitance you should never go 'down' by much and it's better to be the same or slightly higher. Depending on the situation.

There are tons of brands, there are tons of temperature ratings as well, for a tube amp it's best to get the 105degC rated ones, as they get pretty hot with tubes heating the chassis etc.

The brands often preferred for tube amps are F&T or if you can find new stock the Sprague Atom's (but they're pricey) but really the newer radial power supply types perform wonderfully and are significantly smaller for the same capacitance and voltage ratings... if you can use them, it's often better... but in Point to Point I think they're often less preferred, but not unusable.

There are tons of other more 'esoteric' parts of this type of selection as some believe the specific component needs to be of only very limited brands etc, but I am more of the opinion that if it's the right voltage rating and capacitance then it's good to go.

There are MANY other variables that may not be easy to guess at or help on, without a layout and schematic of what you plan to build in the chassis.

~Phil

[Phil_S]

I'm not an expert on this, but that won't stop me from offering my opinion. If you are working with 20uf, 22uf, or 25uf, these are all close enough that you should find them to be interchangeable. As the other Phil points out, pay attention to voltage and temperature ratings. Don't replace a 450V cap with a 350V cap. That's just begging for trouble. There are so many brands out there it can get very confusing. I suggest the name brand caps don't cost that much more. If you aren't sure, don't use the cheap stuff and buy your caps from a reputable seller. This will help protect you from inferior (quality) and counterfeit (not what is says on the label) merchandise. Axial caps tend to be a bit harder to find, but they can be found easy enough.

[Mikante]

There you go.
The sprague atom are way to expensive.
Where i buy the components there are no information about which one might be suitable for filtering or not.

[pompeiisneaks]

Yeah stick around 20-25uF and 105degC rated, and 450VDC. If you go lower, the amp may push closer to 450 when the tubes aren't yet warm and conducting and pooof, there goes the cap.

For filtering the only ones 'suitable' are also the 'only ones' basically you can buy either electrolytic OR metal film but metal film, although they'll last a LOT longer, cost like 2-5x the cost of an electrolytic of 22uf/450VDC rating... so since atom's are already too pricey, stick with electrolytics and you're golden.

~Phil

[Mikante]

F1BF24B2-238E-486D-B43D-19706B7A241B.jpeg

Is this ok?
It is a f/t 22uf 450v, but i find no info about the temperature handling.
It seems that “type A” is rated for 85 c.
I m starting to understand the difference in price now.
Would you use these anyway?

[martin manning]

Absolutely. F&T are good quality caps, and very popular for new builds and replacements. https://www.tubesandmore.com/sites/defa ... -a_new.pdf

[Mikante]

Absolutely. F&T are good quality caps, and very popular for new builds and replacements. https://www.tubesandmore.com/sites/defa ... -a_new.pdf

Thank you but that one in the link you just posted is the type AH and is rated for 105 degrees.
I can not find it where i usually shop for components.
I see from the data sheet that the type A will not last very long in a high temperature situation.

[martin manning]

Thank you but that one in the link you just posted is the type AH and is rated for 105 degrees.

At the top of the sheet, note 85C for rated voltage over 100V, and the specifications are listed for Type A. Where are you located?

[Mikante]

Italy, is that what you asked?

[martin manning]

Ok so EU. Banzai Music in Germany sells F&T electrolytic caps.

[Mikante]

Yes, there is where I buy the components. Unfortunaly they do not sell the f+t type ah capacitor, only type a.
They are pretty cheap, not even 10 euros for 4 22uf 450v capacitors.

[martin manning]

Type A is fine. That's what the data sheet linked above is for, and what I get here is US. Perhaps you are overthinking this?

[Mikante]

Thank you.
Yes sometimes i do overthink.
That zone of the circuit board scares me a little to be honest

[pompeiisneaks]

Type A is fine. That's what the data sheet linked above is for, and what I get here is US. Perhaps you are overthinking this?

I did suggest that 105C rated are better for tube amps, so maybe I misled? I have always thought in tube amps with heat the higher temp rating is smarter?

~Phil