Are these the filter caps? (Picture included)

[GRIMESPACE]

Thank you!!!

[Dave Curtis, dB AudioTech]

FWIW, when the PS caps don't have bleeder resistors and the amp is powered down with no tubes in it, the caps will hold their charge for quite some time. The voltage falls off fairly quickly when the tubes are in the amp (this is using the '89 JCM 800/2203 I recently had on the bench as an example). Just make sure you measure the DC voltage before you dive in...

[Steve Conner]

That's right, when the power is turned off, the tube filaments will take a while to cool down, and during that time they'll keep working and use up the remaining charge in the capacitors.

On many tube amps, you can keep on playing after turning the power off, and the sound will slowly fade and fizzle out. When it finally stops making any noise, the caps may well be discharged to a safe level. (don't use the standby switch if it has one, as that could well defeat the purpose)