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Old 11th January 2012, 06:15 PM   #1
mbede is offline mbede  Croatia
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Default Which cathode bypass capacitor?

...would you use in SET amplifier if you had voltage of approx. 100v and 47uF as requirements?
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Old 11th January 2012, 06:36 PM   #2
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The bypass capacitor may be calculated knowing the lower audiofrequency to be amplified without attenuation, and the resistor value which will be bypassed.

C = 1/ (2 * pi * fmin * R)

where F min is the frequency at -3dB, R the resistor above mentioned. Choose almost a 10x value if you want no -3 dB loss. The working voltage, the more closest up to the expected DC voltage across it, ej, for 100V use 150V more or less. Not use 400V !! in this case.

Good luck.
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Old 11th January 2012, 06:38 PM   #3
mbede is offline mbede  Croatia
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Hello, I was actually hoping for a brand/type recommendation! I know I must use 47uF and voltage of somewhere 120-160v.
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Old 11th January 2012, 06:40 PM   #4
DF96 is offline DF96  England
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The calculation should use the parallel combination of cathode resistor and 1/gm.
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Old 11th January 2012, 07:58 PM   #5
dhaen is offline dhaen  Europe
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Default My opinion

Forget about the "boutique" types, buy one branded by one of the major EU/US/JP manufacturers that has low ESR and a high temperature rating.
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Old 11th January 2012, 08:37 PM   #6
M Gregg is offline M Gregg  United Kingdom
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Cost for SE is quite cheap..

I would use either:

(ELNAS-091) - 47uF 100V Elna Silmic II Electrolytic Capacitor
(ELNAC-090) - 47uF 100V Elna Cerafine Electrolytic Capacitor
Depends on the sound you want..

If the working is 100v I would go higher voltage.. something like Mundorf M-lytic


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M. Gregg
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Last edited by M Gregg; 11th January 2012 at 08:44 PM.
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Old 11th January 2012, 09:23 PM   #7
M Gregg is offline M Gregg  United Kingdom
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The only other thing I would do,

Is make sure the working temp is correct for the location..
Also not connect the cap direct to the cathode resistor..

It is possible to get 400V 105 deg Rubycon from Farnel..

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Old 11th January 2012, 09:59 PM   #8
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Quote:
Originally Posted by M Gregg View Post
Also not connect the cap direct to the cathode resistor..
Why's that? Never heard of that before.
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Old 12th January 2012, 07:01 AM   #9
dhaen is offline dhaen  Europe
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Quote:
Originally Posted by simon2a3 View Post
Why's that? Never heard of that before.
To keep the capacitor away from the hot resistor.
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Old 12th January 2012, 07:09 AM   #10
mbede is offline mbede  Croatia
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Hello Gregg, what would be the difference in sound of Elna cerafine vs. Silmic II?
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