To form or not to form high voltage filtering caps?

[mac]

I rememeber that some decades ago high voltage electro caps must to be formed with a variac to get the most from them.
I wonder if it is a good practice today. And if the answer is yes, how to do it WITHOUT a variac.

I have to filter 220V ac to 220V dc. I am thinking of a 10M resistor in series with a 100uF 450V electro cap, both connected after the 1n4007s rectifiers. This way the cap will get fully charged after RC=15 minutes. Is this method ok, is it slow enough, etc?

mac

[JonFrum]

If the caps are new, I wouldn't bother. If they are at least a few year old, check out the GEO Tube Amp FAQ - I'm pretty sure it's discussed there.

[Peter Snowberg]

I buy caps that are already formed.

There should be no need to do additional forming to new caps that are used within ratings. With old caps you take your chances.... with additional forming, or without.

[R.G.]

Tube amp FAQ, Geofex.

[mac]

Caps are new but i don't know if they were on the shelf for a long time. It is hard to get quality parts down here, especially high voltage caps with printed day of manufacture. 

Tube amp FAQ, Geofex.

I forgot to read 'the bible'. 

mac

[Paul Perry (Frostwave)]

The latest (Dec 2006 page 7) copy of Silicon Chip magazine (Australia) has an account of a valve guitar amp using a rarish "3 in 1" electrolytic filter cap that exploded in use, after being reformed...

[mac]

The latest (Dec 2006 page 7) copy of Silicon Chip magazine (Australia) has an account of a valve guitar amp using a rarish "3 in 1" electrolytic filter cap that exploded in use, after being reformed...

I'm going to read that, thx.

mac