Valve question

[9 volts]

I've just done a test where I removed one output valve and tested it. This produced the same hum only louder. I'm figuring that this may show that either one valve working poorly or the pair are badly matched. I'm just guessing here. Make sense? (ps- More reading has revealed that if it was microphonic there would be squeal sounds rather than hum). Sorry about the spelling in the last post.