Can I use polarized capacitors instead of non-polarized caps?

emretelci

Member
2015-10-23 12:17 pm
(By the way, this is not a general question, I want to learn if I can use polarized capacitors instead of non-polarized caps for this circuit.)

I know that using better caps are always good so I have bought some expensive auricap capacitors for the vacuum tube pedal I am building. But when they have arrived I have figured out that the caps are polarized. On the schematics, the original caps are non-polarised, so I want to ask if I can use polarised ones instead of non-polarised caps. (If I can, which way I should connect them)

The caps are 0.1 uF and here is the schematics. I have circled that caps in yellow...

[IMGDEAD]https://www.emre.co.uk/wp-content/uploads/2016/06/caps.png[/IMGDEAD]


Thanks for help...:rolleyes:
 
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On the left one, one would usually put a polarized cap with the negative out to the world. The rightmost output one the negitive would go out. The other 0.1 uf, follow the DC voltages printed and point the cap the correct direction.
I would think polarized aluminum electrolytic extremely rare in 0.1 uf size. Most of these are plastic dielectric these days. A ring around one end does not indicate polarization, but instead indicates the outer wrap terminal for radio frequency applications.
I wonder where the minus .5 v on the tube grid is coming from, as there is no minus battery. Usually to save money on power supplies designers put a resistor between the tube cathode and ground to boost the cathode up above zero and make the grid negative with respect to the cathode. I don't see a cathode resistor here.
 
emretelci said:
I know that using better caps are always good
Using 'better caps' is a good way to give money away. For a circuit which presumably is intended to distort they make no difference at all. You could have used cheap polyester caps.

indianajo said:
I would think polarized aluminum electrolytic extremely rare in 0.1 uf size. Most of these are plastic dielectric these days. A ring around one end does not indicate polarization, but instead indicates the outer wrap terminal for radio frequency applications.
Yes, very unlikely that 0.1uF caps are polarised.

I wonder where the minus .5 v on the tube grid is coming from, as there is no minus battery.
Probably grid current. This may be a significant part of the distortion introduced by the circuit.
 
All 4 capacitors highlighted are signal passing "coupling" capacitors.
These are required where the two sides are at different DC voltages.
A non polar plastic film chosen to exceed the worst case voltage across them will do well here.
The value should be chosen to pass all of the audio. Aim for a passband about one decade lower than the lowest frequency you want to pass.
Since it is valve/tube the worst case voltage differential could reach B+ and so I would recommend 400V, or 600V, capacitors. 100nF should cost well under 50cents (0.30 GBP).
Save your expensive handmades for some other deserving duty.

You can only use polarised for coupling duty, if they never see a reverse voltage. That depends very much on the circuit, the AC voltage peak could exceed the DC voltage and put the capacitor into reverse mode. I would not use a polarised capacitor here unless I knew exactly how the circuit worked to ensure I could calculate the worst case reverse voltage.
Use a plastic film capacitor MKS/MKT/MKP, are all metalised film and all are suitable.
 
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rayma

Member
2011-04-29 8:37 pm
Yes, I already have cheap ceramic caps, but just for the sake of learning, are the auricaps
polarised and can I use them even if they are polarised.

Film capacitors (including these) are NOT polarized. The outside foil's preferred connection
is not related to polarization.

Only electrolytic or tantalum capacitors are polarized, and these types could be damaged
if connected improperly.