Fizz Cap

[C Moore]

What exactly does the "fizz" cap do.?
I am referring to that cap across the plate load of a phase inverter.
Typical was the (I believe) 48pf cap on a Marshall model 1986-1987.
Thank You

[martin manning]

The signals on the two plates are ~equal and 180 degrees out of phase. Connecting them with a small cap will cause high frequencies to be cancelled. 47pF looks like a 34k resistor at 10kHz.

[C Moore]

10-4

If I knew the formula.....I could do the math.
10k is pretty high (I think) for guitar.
What happens to that resistance as the frequency decreases and approaches 6k.?
Thank You

[martin manning]

Multiply by 10/6... 56k. The formula for capacitive reactance is 1/(2 pi f C)

[C Moore]

Xc
That is right.
Thank You Again