Why does the cathode bypass cap always use high-voltage in tube amps?
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Why does the cathode bypass cap always use high-voltage in tube amps?
Most tube amplifiers use bulky high-voltage capacitors whenever they are not electrolytic capacitors when applying a cathode bypass cap.
Actually, the voltages applied to the cathode are less than 50v, so why use such bigger ones?
Is there a problem with using a small film capacitor that just gets into the Stompbox effector?
Actually, the voltages applied to the cathode are less than 50v, so why use such bigger ones?
Is there a problem with using a small film capacitor that just gets into the Stompbox effector?
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
Because it's MOJO
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
No real reason other than what they've got to hand. I use 25V capacitors generally.
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
The fact is that when you use a cap of over rated voltage they last longer and higher voltage levels and physical size go hand in hand!
Caps also have a max AC voltage rating ( as in signal level ) that is more times then not equal to 1/2 of its DC voltage rating.
Caps also have a max AC voltage rating ( as in signal level ) that is more times then not equal to 1/2 of its DC voltage rating.
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
The smallest 25uF film capacitor I could find (in lowest DC voltage)...has a 37.5mm lead spacing. A .68uF 100V film cap is ~20mm L. 25V and 50V electrolytics are MUCH smaller....
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
I don't understand what you are referring to?psychepool wrote: ↑Thu Nov 16, 2017 7:26 amMost tube amplifiers use bulky high-voltage capacitors whenever they are not electrolytic capacitors when applying a cathode bypass cap.
Please can you provide some examples of this?
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
Yes, I too was confused, most tube amps I've seen either use 25V or 50V electrolytic bypass caps... maybe I'm misunderstanding something?pdf64 wrote: ↑Thu Nov 16, 2017 6:45 pmI don't understand what you are referring to?psychepool wrote: ↑Thu Nov 16, 2017 7:26 amMost tube amplifiers use bulky high-voltage capacitors whenever they are not electrolytic capacitors when applying a cathode bypass cap.
Please can you provide some examples of this?
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
My guess is Marshall cathode bypass is often 0.68uF, and I've seen 600v caps there, probably because that's what's handy.
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
He is specifically not interested in electrolytic caps. He's talking about smaller caps that you will see in a lot of popular Marshall amps, for example. Like the 0.68µF cathode bypass cap. Those would be huge if using 500 volt caps but they are a very manageable size if only 50v or 100v. I'd like to see some of those amps that are using high voltage caps for that purpose. Low voltage caps are available.
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
I'm sorry for the confusion. It's a question that I thought about converting the Marshall diy amplifier.
I was always wondering what the reason for using the high-voltage was like the .680uF cathode bypass cap on the first stage of Marshall.
When the electrolytic capacitor is used as the cathode bypass cap, 25 ~ 50V is usually used, but when it is not electrolytic capacitor, the high voltage is always used. I wondered about this.
I was always wondering what the reason for using the high-voltage was like the .680uF cathode bypass cap on the first stage of Marshall.
When the electrolytic capacitor is used as the cathode bypass cap, 25 ~ 50V is usually used, but when it is not electrolytic capacitor, the high voltage is always used. I wondered about this.
Re: Why does the cathode bypass cap always use high-voltage in tube amps?
Unless one searches for a good source for thos .68, .47 etc. caps at 100v you usually find larger voltage caps instead.
If I order some part from surplus electronic's company I look around to see if they have lower voltage caps not only for Marshall amps but to use in guitars as well.
Mark
If I order some part from surplus electronic's company I look around to see if they have lower voltage caps not only for Marshall amps but to use in guitars as well.
Mark
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
Oh gotcha, sorry that's why I was confused, I haven't ever done Marshalls, and didn't realize that. Yeah I think as others have said, they're mostly available in those sizes. I did a search and found some CDE ones that look 'okay' in the 200V range, as an example:psychepool wrote: ↑Fri Nov 17, 2017 6:04 am I'm sorry for the confusion. It's a question that I thought about converting the Marshall diy amplifier.
I was always wondering what the reason for using the high-voltage was like the .680uF cathode bypass cap on the first stage of Marshall.
When the electrolytic capacitor is used as the cathode bypass cap, 25 ~ 50V is usually used, but when it is not electrolytic capacitor, the high voltage is always used. I wondered about this.
https://www.mouser.com/ProductDetail/Co ... QZsctgo%3d
But most of the caps that are used for coupling need the higher voltage rating, and I think since many people buy them in bulk if they're doing mass installs, it's just cheaper to use the ones they already have in that same rating/group.
Those kinds exist, so go ahead and use them in those builds for sure. For a one off builder it's likely cheaper.
~Phil
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Re: Why does the cathode bypass cap always use high-voltage in tube amps?
Hoffman sells two brands of low voltage 0.68µF.
Re: Why does the cathode bypass cap always use high-voltage in tube amps?
Define "low voltage"
Lowest I found were 160V and 250V; I guess OP was expecting 25V and 50V film capacitors.
It won´t happen.
Main problem is that for lower voltage rating you need atoms thick film ... potential for pores or even holes, also tearing (or at least stretching) is very high , not practical below a certain thickness.
While on electrolytics nobody physically makes, even less winds, any kind of film, dielectric is chemically created and can be real thin.
Lowest I found were 160V and 250V; I guess OP was expecting 25V and 50V film capacitors.
It won´t happen.
Main problem is that for lower voltage rating you need atoms thick film ... potential for pores or even holes, also tearing (or at least stretching) is very high , not practical below a certain thickness.
While on electrolytics nobody physically makes, even less winds, any kind of film, dielectric is chemically created and can be real thin.
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