Which cathode bypass capacitor?

mbede · 11th January 2012, 06:15 PM

...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

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 · 08:44 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

Regards
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..

Regards
M. Gregg

simon2a3 · 11th January 2012, 09:59 PM

Quote:

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

Quote:

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?

11th January 2012, 06:15 PM	#1
mbede diyAudio Member Join Date: Dec 2008	Which cathode bypass capacitor? ...would you use in SET amplifier if you had voltage of approx. 100v and 47uF as requirements?

11th January 2012, 06:36 PM	#2
Osvaldo de Banfield diyAudio Member Join Date: Dec 2011 Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina	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. __________________ LW1DSE

11th January 2012, 07:58 PM	#5
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	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.

11th January 2012, 08:37 PM	#6
M Gregg diyAudio Member Join Date: Jun 2010 Location: UK	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 Regards M. Gregg __________________ What is the sound of one hand clapping? Last edited by M Gregg; 11th January 2012 at 08:44 PM.

11th January 2012, 09:23 PM	#7
M Gregg diyAudio Member Join Date: Jun 2010 Location: UK	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.. Regards M. Gregg __________________ What is the sound of one hand clapping?

11th January 2012, 06:38 PM	#3
mbede diyAudio Member Join Date: Dec 2008	Hello, I was actually hoping for a brand/type recommendation! I know I must use 47uF and voltage of somewhere 120-160v.

11th January 2012, 06:40 PM	#4
DF96 diyAudio Member Join Date: May 2007	The calculation should use the parallel combination of cathode resistor and 1/gm.

12th January 2012, 07:09 AM	#10
mbede diyAudio Member Join Date: Dec 2008	Hello Gregg, what would be the difference in sound of Elna cerafine vs. Silmic II?

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