Capacitor questions

[Tyimo]

Hi!

I would like to ask some questions:

1. Sometimes I see in voltage divider mosfet bias circuit a
capacitor connected between the middlepoint of the voltage divider to the ground. Sometimes not.
A, Is this cap really necessary or not??
B, Should be ELKO or foil cap?
C, Is there any rule for calculating such a capacitor's value?

2. Sometimes I see "Accelerator" capacitor on the amplifier PCB, in the input of V+ to ground. Sometimes not.
Sometimes it is a few hundred uF ELKO or a couple of nF fouil cap.
A, Is this cap really necessary or not??
B, Should be ELKO or foil cap?
C, Is there any rule for calculating such a capacitor's value?

3. This is an evergreen question :-)
What kind of input cap is good?
In some cases I see ELKO in the input, but sometimes foil cap.
Which is better?

Greets:
Tyimo

[Tyimo]

Nobody can answer?!?
I cann't believe....

[Nelson Pass]

You must have some patience. Most of the wise guys
around here are old and slow.

[Tyimo]

Yes, Master!
Maybe you could best respond?

Greets:
Tyimo

[Melon Head]

I will answer 3.
No cap is better than film is better than electrolytic
There is more to it than that but i don't want to ramble on

[Tripmaster]

Originally Posted by Melon Head

I will answer 3.
No cap is better than film is better than electrolytic
There is more to it than that but i don't want to ramble on

37...not that old?

[AndrewT]

At least a third of Members are asleep at any time.
At least a third will be doing something else at any time.
Of the remainder, how many would you expect to be online when you post a question?

[Tyimo]

Of the remainder, how many would you expect to be online when you post a question?

I wrote my reasking question after that I saw there was already more than 77 views....
But I am patient.

[Tyimo]

No cap is better than film is better than electrolytic

It is too simple answer.
Look at Mr. Pass's designs! He also use many time ELKO as input cap.

[Gordy]

Originally Posted by Tyimo

Hi!

1. Sometimes I see in voltage divider mosfet bias circuit a
capacitor connected between the middlepoint of the voltage divider to the ground. Sometimes not.
A, Is this cap really necessary or not??
B, Should be ELKO or foil cap?
C, Is there any rule for calculating such a capacitor's value?

If the voltage divider then feeds a large value resistor to the bias point (mosfet gate), then the answer is usually 'yes, a capacitor is sensible'.

Working with the voltage divider resistor, the capacitor forms a RC low pass filter to smooth the bias voltage. Use an electrolytic.

: )