5U4G replacements?

[MassiveBoogers]

Hey guys. I bought my Dual Rectifier a few months ago and ran into a problem last night. I noticed while on my clean channel that I could hear a weird, fuzzy distortion coming through. I checked the other two channels and heard that it was bleeding through on those as well. I then looked at the back of the amp and saw that both 5U4Gs were not glowing but were hot (the 12AX7s looked to be fine). I turned it off for a while and turned it back on to standby mode and nothing changed. What kind of problem am I looking at? Replacement tube(s)? Blown fuse? I'd greatly appreciate the help as I am new to tube amps and don't want to go out buying stuff that I don't need. Also, could anyone tell me what would lead to this or is it just typical after so long that this will happen? Thanks!

 

[Old BF Shred]

The 5U4 filaments should be visible and if they're hot, they are likely working.
Have you tried it on diode setting?

 

[MassiveBoogers]

No I haven't tried that, but I don't understand what you're implying by switching to the diode setting. I'm wanting to know why they aren't working currently as they have been in their current positioning.

 

[94Tremoverb]

If the amp was in the Vacuum Tube setting and it was working at all, the rectifiers (or at least one of them!) are fine. Rectifiers often glow less brightly than other tubes.

If you want to eliminate the rectifier tubes as the cause completely, do as BF Shred said - switch to Silicon Diode mode on the back panel, and (if that doesn't fix it, and your amp is a 3-channel Rectifier) to make doubly sure pull the rectifier tubes. But it doesn't sound like a rectifier fault.

It's also nothing to do with the fuse, since a blown fuse stops the amp working.

Weird fuzzy distortion could be a preamp tube, power tube or something other than tubes. How to find out without spending any money (yet):

To test the preamp tubes, first bypass the effects loop using the switch on the back. Does this fix it? If no, now pull V4 - the preamp tube fourth away from the input jack, which is now bypassed so can't be the cause - and use this one to test the other four positions one after the other.

If that doesn't locate it, pull two of the power tubes - either the inner or outer pair, it doesn't matter which. Now test again. If the problem persists, replace these two and pull the other pair, and test again. If at any time the fault goes away, the bad tube(s) are out of the amp. If none of this cures it, it's not a tube fault.

If it does turn out to be a power tube fault, chances are it's only one and you can identify which by mixing up the pairs until you can be sure which one is causing it. Throw out this one but keep the other three as spares when you buy a new set - you always need spare tubes.

Hope that helps!