[pataburd]

My amp calls for 150uF/400v, but I want to use Black Gates, which I can only find in 150uF/350v.  Is there danger in this substitution?  Or is is "better" to use an Elna 220uF/400v for the same application?  
 
Actually. my headamp was doing fine, for several years, with the Black Gates mentioned above.  However, the last technician who worked on the amp was emphatic about switching them out (with an inferior component) and making sure they were exactly to specification.

 

[Avro_Arrow]

The voltage rating is the highest voltage a capacitor should be used with.
If you exceed the working voltage there is the risk of an internal short and
catastrophic failure of the capacitor.
However, good designers over rate the voltage value on by a factor of two
when designing a product (Amp).
If the value you have been using is still working, then there is no reason
to change it.

 

[cobaltmute]

I would add to what Avro_Arrow said.

You want to choose your rating based upon what you'd expect capacitor to see in the worst case and then add 2x.

If it is a power supply capacitor, you want to be generous.

 

[pataburd]

O.K.
I checked online.
Will go with the Elnas.
 
Funny, I posted this reply first, but the two messages above showed up afterwards and "wedged" themselves inbetween.  Thank you A_A and cm!
 
The Elnas are en route.  I've read good things about the Silmic II, but these are just the "regular" Elnas on order.