Discharging power capacitors

I'll just add to the good suggestions above that with some types of capacitors it may be a good idea, after the capacitor appears to have been discharged, to remove the voltmeter or other means of discharge, wait a while, and then reapply it for some amount of time.  The voltage on some capacitors that appear to have been fully discharged can subsequently "bounce back," to a small fraction of the original voltage but one that nevertheless may be significant, as a consequence of dielectric absorption.

Best regards,
-- Al

Depends on the Voltage - if a tubed amplifier you should be EXTREMELY careful - voltages inside are lethal - always work with one hand in your pocket.  

But as described above use a bleeder resistor - 1Mohm definitely if a tubed Amplifier , a SS with much lower voltages you can use one of considerably lower resistance - I for an example use a 25W 50 Ohm resistor for bleeding the rails fast when working on my amplifiers, rails are between 35VDC and 65VDC 9 (The internally installed bleeders are 22K)

Best of luck 

Peter