Help! Mark V started buzzing loudly suddenly at practice

[primeholy]

Help! Mark V started buzzing loudly suddenly at practice. What could it be? I installed some new preamp tubes this weekend.

[eudaimonia02912]

Probably a tube. Could be a power amp tube, too. Does it happen on all channels or just one? Does it happen in all wattage modes? Does it happen in channel 2 when the loop is hard-bypassed?

 

You might be able to narrow it down without having to replace the tubes one by one.

 

Too bad you've got this problem with new tubes. I recently ordered a set of seven tubes from a well-regarded dealer, and two were dead on arrival. Alas.

[Wizard of Ozz]

Bad preamp tube. Replace each one, one at a time, with a known good tube to isolate. More than 1 tube could be bad.

[primeholy]

All channels. Haven't bypassed loop yet.

[BlackCustom]

Have you tried turning down the "buzz" knob? (There's gotta be one on that amp somewhere).

[TruSlice]

[primeholy]

Let it cool down and worked for about 5 minutes and started again. Guess I'm done 4 the night.

[fretout]

Sounds like a preamp tube. What are you running for the Phase Inverter? 12AX7? SPAX7-A? 12AT7?

[primeholy]

 

Sounds like a preamp tube. What are you running for the Phase Inverter? 12AX7? SPAX7-A? 12AT7?

 

 

Whatever mesa put stock in there is there. I have a ruby 12ax7ac7 in v1 and v7 which I just got and put in about a week ago. Tonight was the first time I played longer than ten minutes and got it up to band volume since putting those in.

[primeholy]

And thanks everybody who chimed in:thu:

[Spaced Out Ace]

I'd say it was the preamp tubes you put in, old preamp tubes that're getting like a cranky old man, or perhaps a power tube, in that order of likely hood. Ask for a replacement.

[Zozobra]

Pull the PI tube and power it up. If it still buzzes then its something in the power amp. If its not the power amp put the PI back in pull the nearest pretube to the PI and power it up - rinse and repeat through all the pres until the buzzing goes. This will tell you where in the amp you have the problem so you can narrow it down to a bad tube or at least which part of the circuit is playing up.

[Spaced Out Ace]

Pull the PI tube and power it up. If it still buzzes then its something in the power amp. If its not the power amp put the PI back in pull the nearest pretube to the PI and power it up - rinse and repeat through all the pres until the buzzing goes. This will tell you where in the amp you have the problem so you can narrow it down to a bad tube or at least which part of the circuit is playing up.

 

I'm gonna look n00b as fuk but... you can do that?!

[Zozobra]

Sure, all it will do is stop that part of the circuit passing signal to the next. When you build an amp one of the first tests you do is to power it up with no tubes in so you can measure voltages at certain points to make sure you havent {censored}ed up. Its not ideal to run like this for extended periods of time since the power transformer is unregulated so it will output a higher voltage than expected under loaded conditions which some components might not like if they are close to their operational limits.

 

In this case it will be immediately obvious if the noise has gone so the amp only needs to be on play for 10 seconds tops.

[Spaced Out Ace]

Ah, cool. Learn something new everyday.

[primeholy]

I just noticed when it was buzzing 3 of the power tubes started glowing bright blue.

[Zozobra]

6L6s? Like this:

 

Thats nothing to worry about. Its just stray electrons whizzing past the plate and striking the glass. You'll notice that when your amp isnt buzzing the amount of blue glow is dependant on how hard you play.

[primeholy]

I wasnt getting an input signal after replacing v1. Turns out I broke the glass tip on the top of the tube:mad:

[primeholy]

I replaced the new preamp tubes with the old ones and swithced out the power tubes with some from my IV I used to have. Same thing happened. Im not done swapping preamp tubes(although it is a pain:mad:). Is there any way a rectifier tube would do this?

[Spaced Out Ace]

 

http://acruhl.freeshell.org/mga/main/troubleshoot.html 3. Change the tubes The filament in a tube can cause hum. When tubes get old, sometimes they hum. Try unplugging tubes going from right to left looking from the back. When you pull out a tube that reduces or eliminates hum, try a new one in that position. The rectifier tube could be causing hum as well. Sometimes in a 4 power tube amp, one power tube will fail and this will cause the amp to hum.

 

 

...

[primeholy]

 

...

 

 

Im doing that , but I have to power down and pull power tubes to get to my preamps. This amp has {censored}ing 7 preamp tubes:mad: I dont have a spare rectifier tube. The hum starts about 5 minutes or so of playing.

[Spaced Out Ace]

You said 3 PTs were showing the blue on the glass. I thnk one of them failed.

[Spaced Out Ace]

I just noticed when it was buzzing 3 of the power tubes started glowing bright blue.

 

What was the fourth one doing?

[primeholy]

 

What was the fourth one doing?

 

 

It looked normal, but with the different power tubes I think only two were bright blue when the buzzing was happening.

[Spaced Out Ace]

 

It looked normal, but with the different power tubes I think only two were bright blue when the buzzing was happening.

 

 

Since I can't inspect it myself, I'd just call Mesa and see what they say. At this point, I say just order tubes from Mesa and see if that solves the problem.