Chan 1 distortion

[andyp13]

Hope someone can help
I recently revolved my MK V with JJ's and it has been sounding fine, however, yesterday Chan 1 (I only use chan 1) was distorted and also seemed very thin, I had to increase the bass and decrease the treble, it was very distorted dispute the setting being on Clean, full power etc (all the settings for the cleanest sound).
Could anyone suggest what the problem could be?
Could it be a valve? If so which one?

Also what does the 5U4G valve do? Nobody seems to know.

TIA
Andy.

 

[shredding]

Check v1 and v3. 5u4g is the rectifier tube.

 

[domct203]

Also what does the 5U4G valve do? Nobody seems to know.

TIA
Andy.

As mentioned, the 5U4GB (5U4G) tube is your rectifier tube. It converts AC voltage to DC voltage.
From page 42 of your owners manual:

I do not know why you feel that "Nobody seems to know"?

Dom

 

[FastRedPonyCar]

Put the original tube back into V1.

Also, where is the fx loop volume knob set. Turn it all the way up if you're using the loop. If you're not using the fx loop, try flipping the switch to disable it. The amp's volume will triple.

I use my clean channel in tweed mode with the gain relatively low and the volume moderately high and always in 90w mode with the bold setting engaged. massive clean headroom.