I'm using "Hughes and Kettner: Statesman QUAD EL84" tube amp and it started sounding more quiet than usual.

When i turn the volume knob to max it sounds like it was on 40 % before malfunction.

Perhaps someone can tell what should i do? Will changing tubes help?
Power tubes are about to go boom, probably.

Lucky you, EL84s are cheap as shit.

I'd replace them before they go boom. IE: ASAP.
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Yep, sounds like you need new power tubes.
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I recommend JJ power tubes. Best sounding EL84 Ive tried that aren't a vintage or NOS tube.
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Agreed on the power tube issue and the JJs. JJs are the only tubes I trust nowadays. The other thing it could be if it isn't the tubes is an output transformer, but I'd do the tubes first.
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