the terminology with this is confusing. I found myself getting a little confused reading slipin's post since he said he agreed with fuzzbox but then seemed to contradict him.
Just to clarify in case other people are as dense as me - if the amp is in standby mode (i.e. standby mode turned on), there will be no sound to allow the tubes to warm up before being stressed. If the amp is out of standby mode (i.e. standby mode turned off), sound will come out of the amp.
On my amp (and perhaps yours is the same), the power and standby switches are side by side and you turn both of them up for sound. So for power, this means "on" is up, but for standby, "off" is up.
Perhaps a better way to think of it is "sound on/off" for the standby switch.
I start out with both power and standby down. First I flip the power switch on. Then I get myself situated with my guitar, cable, etc. and allow the tubes to warm up for a minute or 2. Then I flip the standby switch up. Powering down, I'll first flip the standby switch down and start putting my stuff away. By time time I'm done with that, the tubes will have cooled down a bit and then I flip the power switch down.
As an aside, this reminds me of hookswitch terminology with telephones. In the US, you go "offhook" (pick the phone up off the hook) to make a phone call. Howerver, in the UK and other places in Europe, you go "online" (still picking the phone off the hook) to make a phone call. On and Off can mean the same thing depending on who you are talking to :-).