Possible tube issue

[captain_jim]

I am getting a hum whenever I use the Burn channel on my Express 5:50. It isn't the guitar since I've checked that. One the the pre-amp tubes is to alot brighter than the other pre-amp tubes. However, all the other pre-amps tubes are barely visibly glowing. All the pre-amp tubes are Russian 12ax7s but the one that is glowing more than the others is Chinese. Is that normal?

And, the colors on the power tube are different. I'm at work so I don't know the exact colors of the tubes, but could the power tubes being mismatched be causing that hum or is it most likely a pre-amp tube (if at all a tube) since it only happens in the one channel?

Thanks!

 

[MrMarkIII]

What do you mean by "colors" on the tubes?
The power tubes are indeed matched (in pairs) by color, so if one is labeled red and one blue they could be mis-matched.
Don't go by "glow", that usually doesn't mean much, if anything, especially when comparing different brands.

 

[captain_jim]

By "colors" on the power tubes I mean that their ratings are different. I don't think it would make a big difference but I was wondering if it could be causing the hum issue. I've done some research and it seems that it wouldn't make a diff. unless the tubes themselves were bad. It would seem that I'd need to get some preamp tubes to test since that seems like the most likely culprit.

The big thing is that one of the preamp tubes, the Chinese and only Chinese tube in the preamp (they are all stock tubes that came with the amp), the filament is glowing more than the other preamp tubes (in standby and while on - minus the blue glow that the power tubes have). The one preamp tube is glowing the same amount as the power tubes but all the other preamp tubes are hardly glowing (filament wise). Is that normal? is the big question. Thanks again!

 

[captain_jim]

Another thing, the hum happens in Class A and Class A/B so the power tube mismatch wouldn't be causing the hum.

 

[212Mavguy]

The difference in amount of visible heater filament glow between the Chinese and Russian preamp tubes is a non issue. Different color code/current draw ratings on the power tube pairs is not how Mr. Smith wants your amp to operate. Get a new set of power tubes that are properly matched within a bias range that is workable for your amp. Know what the boundaries of your amp's warranty is when buying tubes and stay within warranty boundaries at least until it expires. Mesa tubes are not very expensive. See a qualified Mesa tech about the hum issue, hopefully your amp is under warranty still.

peace.

 

[stokes]

In a push/pull out put,properly matched output tubes cancel hum that is inherant in a tube circuit.It doesnt matter if the amp is in "class A" or "class A/B" if the tubes are mismatched to the point that they arent cancelling the hum,it will hum in either setting.I aint saying the mismatched tubes are 100% the cause of your hum,but if they are not close enough,they wont cancel the hum as they are intended to do,and are the first place to look.

 

[captain_jim]

Thanks alot for info guys. Very appreciated.