I used 1000v insulated electricians screwdrivers, as I like to be safe when working on electronics that have a higher risk of zapping me.

Amplifiers can have a high current stored in the large internal capacitors. Even with the insulated screwdrivers, please be sensible and ensure the amplifier is unplugged and try to leave it without power for a day or so. Also, read up on working with capacitors before you start work.