Loud squeal from speakers - KEL84

[hunterwd]

Hi Folks

Hope you can help

I have a kel84

I used this about a 2 weeks ago and all was well but decided to connect my other amp up instead.

Went to try the amp again yesterday and when i turned it on the red light didn't change to yellow and a horrible squeal came from the speakers.

Very worrying. I just tried it again using different speakers as i don't want to damage my decent ones and its still happening.

Any idea whats causing this?

Thanks
D