So pulled the chassis on the Blackstar HT Studio 20 for diagnostic relating to the intermittent buzzing as the amp warms up. Checking the output bias it was a little on the cold side so adjusted. The noise was only affected by the master volume control so suggesting the issue lies with the output section. As the bias was tweeked the buzzing ceased & hasn’t yet returned. Do we need a new pair of output tubes is the question❓
Lets leave it to cook for a while.
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