BHK Volume variable when cold

Audio Components Amplifiers
1

Hello

I’ve got an ex demo BHK250 and I’m finding when I first switch it on the volume varies a little up and down for about 10 mins. Is this normal or maybe a symptom of tubes needing replacement?

Thanks.

2

I haven’t heard anything like this. If it’s a demo unit, it probably has quite a few hours on it and could use some fresh tubes.

I’d be surprised if there is a big enough difference in these 10 minutes for one to perceive a noticeable difference. I’d want some measurable data.