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Thread: power supply capacitor size in tube amps

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    power supply capacitor size in tube amps

    The F&T caps we get online are pretty big compared to other electrolytic caps you can get these days. I bought some (think it was panasonic) radial (since they don't sell axial this spec) 10 and 22uf 500v electrolytic caps. They have to be 1/4 the volume of the F&T caps. I don't have any dead ones to cut apart to compare.

    Why are the F&T caps so big, and does anyone use the modern smaller ones in tube amps? Its going to be a bit of a pain to mount and wire them up to, say, and eyelet or turret board, since they are radial, but is there any electrical reason not to use them? They are 105C and 10k hour, so I think they are better spec than the F&T caps.

    Thanks.

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    Quote Originally Posted by mikepukmel View Post
    The F&T caps we get online are pretty big compared to other electrolytic caps you can get these days. I bought some (think it was panasonic) radial (since they don't sell axial this spec) 10 and 22uf 500v electrolytic caps. They have to be 1/4 the volume of the F&T caps. I don't have any dead ones to cut apart to compare.

    Why are the F&T caps so big, and does anyone use the modern smaller ones in tube amps? Its going to be a bit of a pain to mount and wire them up to, say, and eyelet or turret board, since they are radial, but is there any electrical reason not to use them? They are 105C and 10k hour, so I think they are better spec than the F&T caps.

    Thanks.
    As the F&T website (https://www.ftcap.de/en/products/ele...rs/axial-lead/) doesn't show the tube amp versions, I assume that they are custom order types for big amp OEMs and amp parts distributors. Probably size and shape were chosen/specified to make them suitable as drop-in (authentic looking) replacements in vintage type (Marshall etc.) amps.

    There is some temperature benefit from large cans and chassis mounting.

    F&T makes smaller sized axial types with higher temperature/lifetime ratings as well.

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    Last edited by Helmholtz; 07-14-2019 at 11:36 PM.
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    If you think F&T are big, check Sprague Atoms...

    There is no electronic reasonnot to use them; just might have to get creative with the mounting on occasion.
    Justin

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    I have plenty axials 22uF -220uF, 450 to 600V in stock, just pm me if you want some.

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    Quote Originally Posted by Helmholtz View Post
    As the F&T website (https://www.ftcap.de/en/products/ele...rs/axial-lead/) doesn't show the tube amp versions, I assume that they are custom order types for big amp OEMs and amp parts distributors. Probably size and shape were chosen/specified to make them suitable as drop-in (authentic looking) replacements in vintage type (Marshall etc.) amps.

    There is some temperature benefit from large cans and chassis mounting.

    F&T makes smaller sized axial types with higher temperature/lifetime ratings as well.
    Thanks Helmholtz. I thought they were these:

    https://www.ftcap.de/fileadmin/user_...oren/A2012.pdf

    size is same as what Im holding in my hand, only the logo is different.

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    Quote Originally Posted by nickb View Post
    I have plenty axials 22uF -220uF, 450 to 600V in stock, just pm me if you want some.
    Cool, thanks Nick, will do.

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    Quote Originally Posted by mikepukmel View Post
    Thanks Helmholtz. I thought they were these:

    https://www.ftcap.de/fileadmin/user_...oren/A2012.pdf

    size is same as what Im holding in my hand, only the logo is different.
    Oh, I thought you mainly meant the large upright chassis mounting cans.

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    Another thing is that aside from looking like the original size, you want the leads to be long enough for replacement parts in older stuff. You don't want to be needing to add wires to make the leads reach. Same with tiny modern resistors. I order resistors sometimes, then when I get them I think, dang, I should of checked to make sure they weren't too small !

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    F&T tend to be larger in size than IC of the value. Given the reliability of F&T and the known failure rate of IC caps, maybe there is a corelation there. It's enough for me to stick with F&T and deal with it should they need some creative mounting.

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    It's weird, because it WAS working fine.....

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    I would guess the Panasonic caps are superior to the F&T caps if they are 105 degree rated at 10,000 hour lifetime.

    On the question of whether any people use these in guitar amps, yes. I think modern builders that appreciate modern high quality capacitors would use them regularly. they are much cheaper and their specs are better. I think when people want to use the old school style axial caps they mostly want to mimic the look of old amps. I say I think because it's basically just an opinion. Perhaps they want bigger parts to fill the bigger footprint and make wiring it easier like other people mentioned, maybe they want to buy a cap for $7 so they can do a bigger parts markup vs. getting the same cap as a panasonic or united chemicon for $2.50 While some parts have certainly become worse with the passage of time (tubes), I would think that capacitors have only become better from 1960s/1970s to present.

    I like the united chemicon KXL and KXJ series personally. Small size and inexpensive with 10,000-12,000 hour lifetime

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    Last edited by nsubulysses; 07-15-2019 at 07:44 AM.

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    Thanks everyone!!! So, for a hack build, I thought Id use the small/modern better spec'd caps, and just put pairs of turrets close enough together to wrap the leads around each turret, then lay the cap down and put a dab of hot wax to hold them in place. But I wasn't sure if there was something about the electrolyte that these amps "like", sounds like "no" its just ... well modern stuff is modern. For these little tinkering projects I have, it takes the filter capacitor total cost down from 30 bucks to about 6 or 7 dollars. that's enough left over for TWO large meatball parmesan sandwiches at Monicas!!!

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    Quote Originally Posted by nsubulysses View Post
    I would guess the Panasonic caps are superior to the F&T caps if they are 105 degree rated at 10,000 hour lifetime.

    On the question of whether any people use these in guitar amps, yes. I think modern builders that appreciate modern high quality capacitors would use them regularly. they are much cheaper and their specs are better. I think when people want to use the old school style axial caps they mostly want to mimic the look of old amps. I say I think because it's basically just an opinion. Perhaps they want bigger parts to fill the bigger footprint and make wiring it easier like other people mentioned, maybe they want to buy a cap for $7 so they can do a bigger parts markup vs. getting the same cap as a panasonic or united chemicon for $2.50 While some parts have certainly become worse with the passage of time (tubes), I would think that capacitors have only become better from 1960s/1970s to present.

    I like the united chemicon KXL and KXJ series personally. Small size and inexpensive with 10,000-12,000 hour lifetime

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    Beautiful amp! Side question, when we build these amps with eyelets and hand wiring on the board, we use like 22 ga wire. How do you ensure that you get at least that on a PCB board trace? Does it matter if the trace is very thin and wide, rather than more square like a piece of wire is? I started reading up on some of the PCB software, got lost in the details.

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    "Side question, when we build these amps with eyelets and hand wiring on the board, we use like 22 ga wire. How do you ensure that you get at least that on a PCB board trace?"

    Apart from the heaters, speaker outputs, and some conductors in the power supply there is very little current going through most of the wires, so the 20 or 22awg is mainly used for mechanical strength and ease of handling. PCB traces can be much smaller where only small currents are present.

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    Last edited by Bloomfield; 07-15-2019 at 07:22 PM.

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    Quote Originally Posted by Bloomfield View Post
    Side question, when we build these amps with eyelets and hand wiring on the board, we use like 22 ga wire. How do you ensure that you get at least that on a PCB board trace?

    Apart from the heaters, speaker outputs, and some conductors in the power supply there is very little current going through most of the wires, so the 20 or 22awg is mainly used for mechanical strength and ease of handling. PCB traces can be much smaller where only small currents are present.
    Replicating the effective circular mil area of 22AGW solid wire in a PCB trace, the width of that trace gets pretty wide, depending on the thickness of the copper on the board. From a chart I looked at showing the American Wire Gauge & Circular Mils, 22AWG has a diameter of 0.0253", and the area given in circular mils differs from the normal formula for that of a circle (pi*r^2)....given as 642. I'll use pi*r^2 for the area, which would be 0.000503sq in. Then, depending upon what the real thickness of copper foil is for, say, 1oz copper on a board, that copper thickness is typically 0.0014". If we divide 0.000503" by 0.0014", we get 0.359" for a width.....a trace width of 0.359" for 1 oz copper. For 2 oz copper, typically being 0.0028", the trace width would be half that width, or 0.180".

    Needless to say, when we're looking at the range of trace widths on typical PCB's, their equivalent wire sizes get a lot smaller than we'd normally chose when hand-wiring solder turrets!

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    Last edited by nevetslab; 07-15-2019 at 10:07 PM.
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    But to be fair, there's very little signal current flowing in a typical tube amp (outside of the power amp), so even 22ga is probably overkill.

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