Recently I saw a folk duo doing a small pub and they only had room for one PA speaker, so they plugged just one speaker in.

Now many years ago I was told that you could 'do some damage to the amp' and that you should always plug a jack into the empty socket in the amp - even if you didn't plug it into a speaker.

is this an old electricians tale.

I need to know cos I'm thinking of doing the same gig and it is very small.