Which cathode bypass capacitor?

[M Gregg]

Originally Posted by simon2a3

Why's that? Never heard of that before.

As dhaen says..

EG mount the cap on its own tag board connections and link to the resistor (even a short link is still better than direct on to the resistor leads) if the cap acts as a heat sink its life will be short.. + a hot cap can have a different sound..

Regards
M. Gregg

[M Gregg]

Originally Posted by mbede

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

I think its more a case of how each interact with the rest of the circuit..and tube you are using..taste etc.. One is warmer the other is brighter..<<detail is different in how its presented..if you click them in my post they are linked to HIfi collective just for an eg of price (I have no connection) there is a link on the page (small writing) that will take you to manufactures info and a short blog..

They are so cheap you could try both and see...just remember that a 1 hour test is no good give it a week for each..

Black gate would also be a good choice the trouble is getting them and cost..

Regards
M. Gregg

[RajkoM]

Hi Marko.
I saw that you are fan of exotic components with astronomical prices. You should ask C. Van Haus to make CuTf or TfTf capacitors for you

Seriously, 47uF/160V/SET.... output tube cathode bypass, I guess.
For me, forget electrolytics. Also forget any MKPs, because it sounds too harsh (Solen), harsh (Ansar) or too "sssssssss" (Supreme).

My recommendation:

1 - Siemens MKV 125Vac (B25811 type). I use NOS 2x15uF in parallel. If I know well, today Epcos B25811MKVs products in Russia for the Russian market only.

2 - Bosch/Siemens/SEL MP type. These capacitors are huge and need more space for them.

3 - Russian MBGO 160V (only MBGO, not others).

4 - No four.

Best diying

[simon2a3]

Originally Posted by M Gregg

As dhaen says..

EG mount the cap on its own tag board connections and link to the resistor (even a short link is still better than direct on to the resistor leads) if the cap acts as a heat sink its life will be short.. + a hot cap can have a different sound..

Regards
M. Gregg

Fair point. Everything I build is breadboarded so I never really consider the long term issues, plus everything's open so the heat escapes. One day I'll use a box though so it's well worth remembering, for output valves at least.

[ThorstenL]

Hi,

Originally Posted by mbede

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

I would suggest to convert to fixed or semi-fixed bias instead and put a high quality capacitor in the final power supply position.

If for reason self bias must be kept I would use a high quality film capacitor.

However I would connect an additional capacitor with a value of appx. Ck / (Mu-1) between cathode and the +B connecton of the output transformer and I would a resistor of approximately the DCR of the output transformer between the power supply and the +B connection of the Output transformer.

Precise values are best fine-tuned in circuit, with the extra C adjusted for minimum output noise from the Powersupply (this means a very quiet DC supply must be employed) and the Resistor should be tuned for a low frequency response without Bump (output stage only, not complete amplifier).

Ciao T

[RajkoM]

Ciao T.

You mentioned Bump. Talking about self bias, bump is usually a consequence of speaker crossover performance, not value of capacitor in cathode bypass. Such were my experiences.
Something similar with fixed bias ???