Lonestar - Low hum?

[amiller]

My Lonestar Classic started making a low humming noise tonight. It almost sounds like I don't have the guitar cord plugged in. I flipped it to standby and the hum goes away but comes back as soon as I flip it to on. It does the same thing with other guitars and cords. Also, almost no gain on the gain channel. I looked at the power tubes ... none of them look abnormal ... no glowing super bright. I'm guessing it's a preamp tube.

What do you guys think?

 

[amiller]

Hmmm...did a little reading on the MESA site. This could be a power tube issue ... maybe even the Rect tube?

 

[just42dave]

do the pre amp check or try switching to silicone diodes>>?

 

[JTyson]

I was thinking a power tube The last 2 times I had a hum, that was the culprit

 

[amiller]

...try switching to silicone diodes>>?

I woke up this morning remembering that the Lonestare has a diode switch. I'll give that a try this evening....thanks.

 

[glassjaw7]

Could be even worse-an output transformer issue, but most likely not. Let us know!

 

[just42dave]

def I have two mesas and would like to know

 

[amiller]

Could be even worse-an output transformer issue, but most likely not. Let us know!

Yikes! I don't even want to think about that. I also noticed that the hum doesn't start right away. It takes a few seconds before it happens.

I've got a few spare tubes I can swap in to see if I can isolate the issue.

 

[amiller]

So, yes, it was one of the power tubes. Funny thing, when switching from standby to the on position I would hear the hum kick in but none of the tubes glowed red hot.

Anyway, I had a quad of old power tubes lying around that I stuck in the amp just to see if that would cure the hum and gain problem...it did...the hum is gone. The gain is still not 100% (90% maybe). These are old beat tubes so I need to order a fresh set. I think I'll go ahead and get a fresh set of preamp tubes while I'm at it...it's been over a year...maybe two since I replaced any of the tubes.

Thanks for the input.