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mbede 11th January 2012 06:15 PM

Which cathode bypass capacitor?
...would you use in SET amplifier if you had voltage of approx. 100v and 47uF as requirements?

Osvaldo de Banfield 11th January 2012 06:36 PM

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.

mbede 11th January 2012 06:38 PM

Hello, I was actually hoping for a brand/type recommendation! I know I must use 47uF and voltage of somewhere 120-160v.

DF96 11th January 2012 06:40 PM

The calculation should use the parallel combination of cathode resistor and 1/gm.

dhaen 11th January 2012 07:58 PM

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.

M Gregg 11th January 2012 08:37 PM

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

M. Gregg

M Gregg 11th January 2012 09:23 PM

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..

M. Gregg

simon2a3 11th January 2012 09:59 PM


Originally Posted by M Gregg (
Also not connect the cap direct to the cathode resistor..

Why's that? Never heard of that before.

dhaen 12th January 2012 07:01 AM


Originally Posted by simon2a3 (
Why's that? Never heard of that before.

To keep the capacitor away from the hot resistor.

mbede 12th January 2012 07:09 AM

Hello Gregg, what would be the difference in sound of Elna cerafine vs. Silmic II?

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