18Watt.com

...is about caps. I have the need for a NON- polarized cap, specifically a 25 mfd @ 25 vdc in a 5C3 Deluxe build. All I have on hand is an electrolytic at those ratings. If I observe polarity, can I use it? TIA---

You sure you need a non-polarized cap? I don't thyink I have ever seen one that big, if this is to go between a tube's cathode and ground, it should be electrolytic, with the negative end at ground.

...yup, cathode to ground in a 6SL7. Many thanks for your time-

bfwatts wrote:...yup, cathode to ground in a 6SL7. Many thanks for your time-

Nope. just use the poarized and orient the negative lead to ground.

Delete!

You can easily make a non-polarized cap by putting two electrolytics in series, back to back. The total capacitance will be 1/2 of either one of them, but the voltage will be the same as either one.
So if you hook up two 50uF 25V caps back to back (the two pluses together or the two minuses together) you get a non-polarized 25 uF at 25 V cap.
Easy as pie!
Manoteal

Thanks again all, I appreciate the time. Interesting thought on making a non polarized by bootstrapping two e-lytics- I'll have to remember that one!

bfwatts wrote:Thanks again all, I appreciate the time. Interesting thought on making a non polarized by bootstrapping two e-lytics- I'll have to remember that one!

When you buy non-polarised 'lytics for crossovers and such, that's basically what you're buying, but in a single can.

Incidentally, you may like to use 10V or even 6V lytics, rather than 25V ones, since the cathode is only at a couple of volts. You should get improved performance that way.

Merlinb wrote: Incidentally, you may like to use 10V or even 6V lytics, rather than 25V ones, since the cathode is only at a couple of volts. You should get improved performance that way.

I have never heard that one. Improved performance in what respect?

Manoteal wrote:You can easily make a non-polarized cap by putting two electrolytics in series, back to back. The total capacitance will be 1/2 of either one of them, but the voltage will be the same as either one.
So if you hook up two 50uF 25V caps back to back (the two pluses together or the two minuses together) you get a non-polarized 25 uF at 25 V cap.
Easy as pie!
Manoteal

I never heard of that before. Maybe it's possible. Is this fact or just from experimentation ? I'm curious... I've seen non-polarized made from 2 caps, in parallel, then a series diode in front of each cap to keep polarity for each. Obviously not linear.
I know that some caps, such as tantalums, are easily damaged by even a low reverse voltage. The chemical makeup has a lot to do whether they can withstand reverse voltages.

It is indeed possible and is not just my own idea. When we had to make speaker crossovers that required specific values that were hard to get, the back-to-back method does work well.

Think of it this way, if both negatives are connected together, then any positive voltage on the top cap will be 'stopped' from passing through by normal electrolytic function and no reverse current will flow. Connecting a negative voltage on the top cap where some current will TRY to flow to the bottom cap, but then the lower cap will be operating as a proper electrolytic and current will not flow. So either way you hook them up it is still a bipolar electrolytic and without current flowing in either direction keeps the caps from 'blowing up'. You still have to stay within the voltage rating for the lowest cap in series since the voltage will be generally applied to one of them more than the other. And that is why the capacitance is only 1/2 of the total for the two (only one is operating at a time).
In my previous post I said that it would be 1/2 of one of the caps- this is in error. It will be the value of ONE of the caps in the pair.

The other topic about whether a low voltage cap is 'better' than a higher voltage cap is this-
Say you have a circuit that has 12 volts on it and you need to have a cap there. If you use a higher voltage rating than that (like say 50V) the cap will not completely 'form' and you may get a reduced capacitance value. So it is often 'better' to get the closest rating that is above what you need for the circuit, and not something that is 'way higher' (so use a 16 V cap). Of course with very high voltages, it is best to err on the safe side since there are times when voltages often go higher that it is at nominal (like when the power supply is first turned on with silicon diodes and before the tubes start to conduct and bring the voltage down). But at lower values and voltages it is better to get as close as you can in voltage ratings for 'best' performance (which is to say a more accurate cap value in uFarads).

Manoteal wrote:
The other topic about whether a low voltage cap is 'better' than a higher voltage cap is this-
Say you have a circuit that has 12 volts on it and you need to have a cap there. If you use a higher voltage rating than that (like say 50V) the cap will not completely 'form' and you may get a reduced capacitance value. So it is often 'better' to get the closest rating that is above what you need for the circuit, and not something that is 'way higher' (so use a 16 V cap). Of course with very high voltages, it is best to err on the safe side since there are times when voltages often go higher that it is at nominal (like when the power supply is first turned on with silicon diodes and before the tubes start to conduct and bring the voltage down). But at lower values and voltages it is better to get as close as you can in voltage ratings for 'best' performance (which is to say a more accurate cap value in uFarads).

IIRCC, E-Lytics come preformed from the manufacturer? So I don't think forming would be an issue. Fender is still using 25v E-lytics for cathode bypass. My advice would be if you want to use lower voltage caps. go for it. But I wouldn't go thru your amps and change them all expecting some big mojo thing to happen.

I agree. It isn't a big deal and like you said, caps are formed at the factory in most cases and even if they weren't they would as soon as some voltage was applied to them. I was mainly just spouting off. I do that sometimes. . . . . . .
M

p.s. Where would one put a bipolar in a guitar amp? I can't think of a place that it needs to be. Having them in speaker crossovers is nice, since you can't normally use electrolytics and plastic-type caps are large and expensive. But in an amp

Manoteal wrote: p.s. Where would one put a bipolar in a guitar amp? I can't think of a place that it needs to be. Having them in speaker crossovers is nice, since you can't normally use electrolytics and plastic-type caps are large and expensive. But in an amp

I think what got this all started was this schematic. There aren't any polarity signs on the E-lytics.

Cool amp! Are you really going to use octal pentodes in yours? I am sure it will be a screamer.
For caps, count on positive going to the plates and screens and the negatives going to ground unless it is a bias supply for the output tube(s). Then it is reversed.
Rock On!
M

Why would you use octal pentodes in an amp that requires octal triodes? The 5C3 uses 6SC7 dual triodes, conjoined at the cathode, and also a paraphase PI. I bet it sounds awesome. Has anyone heard or played one of these in real life? I would love to know how it compares with a 5E3. Does it have the same early breakup..?

Bluesmechanic wrote:I have never heard that one. Improved performance in what respect?

I guess merlinb is refering to a lower effectuve series resistance (ESR) in lower voltage caps. I doubt the difference really matters that much in a guitar amp.

zaphod_phil wrote:Why would you use octal pentodes in an amp that requires octal triodes? The 5C3 uses 6SC7 dual triodes, conjoined at the cathode, and also a paraphase PI. I bet it sounds awesome. Has anyone heard or played one of these in real life? I would love to know how it compares with a 5E3. Does it have the same early breakup..?.

I think thats a mix up ZP. Anyway I'm wait'n on some eye surgery so I can get back to soldering. Then we'll find out.

zaphod_phil wrote: I guess merlinb is refering to a lower effectuve series resistance (ESR) in lower voltage caps. I doubt the difference really matters that much in a guitar amp.

That makes sense. I can't believe all the cool and usefull info that gets posted on this forum.

Yeah, I have pretty much everything on hand but a chassis, and the 6SL7's...just looks like a fun build, and the octal sockets are LOTS easier for my 50 year old eyes to work on...I don't know anyone who has one of these, but the comments I've heard so far among my player friends have been encouraging. We'll see..

Oops, my mistake! I was just looking at the 8 pin sockets and though that they were pentodes. I guess I really need to pay more attention!
Now I know what it feels like to say something stupid. It is really too easy sometimes in the middle of the night. . .
M