Dark Terror humming noise without anything plugged in

[zombitos]

Hey! First time posting here, I'm new to the whole tube amp troubleshooting thing, first issue i've had.
Anyway, last night i hooked a new pedal to my fx loop chain, a Ditto Looper, i was playing around with it and all of the sudden I got a lot of noise, it didn't went away even if turned off the pedal. So i checked the cables i was using for the fx loop, they were ok, then i tried the amp without anything on the loop (cables disconnected from the back), and there was a faint hum even with volume and gain at 0. I disconnected my guitar (removed cable from the amp input jack) and the hum was still there, i turned up the volume and the gain, the hum noise was not affected by it.
I found out that if i do plug in a guitar and turn the volume up on the guitar, the hum does get louder when the amp volume and gain are increased.
I've been reading about what could be causing the issue, and it seems that it could be a bad tube because is a 60hz hum, i know i'm probably oversimplifying the troubleshooting but I still would like to test the fx loop tube before taking it to a tech.
I don't have any tubes handy, so I was wondering if i could take out the fx loop tube and test the amp without to see if the noise goes away, is that dangerous for the amp? do all the tubes need to be in for the amp to work?
Thanks in advanced for your help!

[zombitos]

I just tried the amp in 7w mode, the humming is still there, also noticed a significant gain loss in both 7w and 15w mode, have to turn the gain knob to 2 o'clock to get any crunch from the amp.

[Jondog]

Probably bad tube(s)

[zombitos]

Probably bad tube(s)

Yeah, I think so too. Do I need to get new tubes to test it, or can I just remove one tube at a time to check for the bad one?

[Jondog]

You need a spare tube to swap in and out of the tube sockets in the preamp section. But more than one could be causing problems. If you change the power tubes (EL84) get a matched set.

[zombitos]

Changing the preamp tubes fixed it!, still has some noise but that's the way the amp has always been, more importantly the gain is back.
I changed the tubes for some Mesa Boogies ones and the amp sounds a lot better than before, should've swapped those tubes before.
Thanks for the help guys!

[Les Paul Lover]

I changed the tubes for some Mesa Boogies ones and the amp sounds a lot better than before, should've swapped those tubes before.
Thanks for the help guys!

It may sound better than before...... But i May be as well that you hadn't realised how worn your (probably power) valves were. The wear is very gradual, usually unnoticeable to the user until it's so worn it's sounds dull, they become microphonic or lose low end / high end sparkle.

New valves should never directly be compared to old valves.

Anyway....... Im Glad you that sorted! Mesa has a solid reputation for valve screening, so that isn't a bad choice.