wouldn't it be
C(Farads) = 1/(2.Pi.F.Xc)
pi = 3.14etc
F = min freq(Hz)
Xc = capacitive reactance(Ohm)
- this is the hard bit, maybe you would have to start calculating
thevenin resistance on the input cct to find the desired Xc.
I thought this page had a fair description -
http://members.tripod.com/~gabevee/mytubamp.htmltho its all for tube amps
a cheap and safe way to try out experimental tube circuits is Orcad
Pspice, the student version is free and plenty of websites have tube
spec files for Psice available.
which leads me to ponder when the 1st soft tube synth is coming out??
andrew
--- In tubesynthdiy@yahoogroups.com, Mark <yahoogroups@...> wrote:
>
>
> Yes, cathode bypass caps often play a role in maintaining a steady
> bias, and depending on the circuit, bypassing the cathode resistance
> can also increase the gain of the tube by reducing negative feedback,
> lower the output impedance, and may prevent oscillation. It charges
> and discharges as the grid changes polarity. Depending on the
> circuit, if the cap isn't large enough, it can reduce its low
> frequency response.
>
> Anyway, I would rather not copy the value another circuit without
> knowing what I'm doing (or what the designer of the other circuit was
> doing). The use and values of cathode bypass caps vary widely, even
> for the same tube. I've found that doing the math, as opposed to
> trial and error, often saves me time and money. Increasing a
> capacitor increases is physical size, cost, and demand on the power
> supply. I'm sure a way to calculate it exists, I just need to find
> it.
>
> On 5/18/07, sasami@... put forth:
> >Just use what you see in other circuit diagrams - frequently 220uF.
Do you
> >understand their purpose? They are there to give what is
essentially a rock
> >solid above-ground DC reference. The only time the voltage across
it should
> >change is while the capacitor is first charging. It charges until it is
> >sufficiently high above the grid voltage that the tube stops
conduction,
> >thus biasing the tube.
> >
> > >Does anyone have any formulae or have any guidelines in determining
> > >the size of a cathode bypass cap?? I am interested in both directly
> > >and indirectly heated cathodes.
> > >
> > >Thanks :)
>