It sounds like you definitely have an amplifier fault. Though I'm intrigued by the comment about the Fane speaker being
much better than the Celestion. Having measured lots of Hacker sets and highlighted the differences between various speaker models (details somewhere on this forum), I would expect it to be slightly different - perhaps a little better as a matter of personal preference - but from your description it's possible the Celestion speaker is not in A1 condition. Which is not unusual... Still, it's all a bit subjective.
Either way, yes, start with the amp - everything you need to know about that has already been said, but shout if further explanations or guidance is required
