Pulling the tubes out of their sockets should not put you in any danger because you will be pulling on the glass part without prying up under the tube socket with a screwdriver or something conductive that might touch the pins.

There are usually resistors wired in parallel with the large caps to discharge them - at least after a couple of minutes after being turned off.

The standby switch may or may not take power off the capacitors, depending upon how the amp is wired. That switch does not even have to take power off the tubes either but usually does.

The bias issue has two ramifications - not burning up the tubes in the case of to little bias (ie. less negative) and not sounding good (ie. bias too negative/too much).

The bottom line is replace the tubes, if they get overy hot or they don't sound good clean, get the bias checked..

Have a great day, Eric Pritchard, Pritchard Amps