capacitor voltage ratings

[Eric Barbour]

>Hi Eric.
>While I'm thinking of it, what voltage should the capacitors be in the
>bandpass. A number of them you haven't specified. Looking at the circuit, I
>figure some (those in the twin T) need to be as high as the power rail (ie
>150v) while others such as the 1 uf on the Q pot can be considerably lower.  
>Cheers.
>Ken


Believe it or not, all of the film capacitors can be rated 100 volts. I've been using
cheap surplus 100v caps in my prototypes, and even though the DC plate supply can
be 150v, the caps NEVER fail. This is because film caps tend to have very
generous underrating, unlike electrolytics. 50% or more underrating is typical at such
low voltages. (Yes, even the coupling capacitor on the plate can be only 100v.
Bear in mind that the idling plate voltage of the small pentode in the VCF or VCA
circuit is only about 40 volts.)

Now, if you were running 400v or more, then you'd have to be more careful about
capacitor voltage ratings........