Filter cap replacement question

[jr_vw2]

How nessasary is it to use a variac when powering up an amp for the first time after replacing the filter caps? I have heard that it is a good idea to power them up slow (over the period of 30 mins) rather than just plug and play so to speak. What are your thought on this? Also what are some other things that I might be able to do to my Peavey 5150 to tighten up the bottom end? Its pretty loose and fartty sounding. Which is typlical of a 5150. I know there are mods out for old silver face fenders where you change the resistance values of a few resistors to achieve this affect. Any light you can shed on this subect would be great. Thanks

[Blue Strat]

A variac isn't necessary but is a nice touch for bringing up any amp to check for shorts, etc.

If that amp uses a solid state rectifier, you can increase the value of the first filtering stage to tighten the low end. If not, there's probably not a lot you can do.

[RussB]

turn the resonance down