HELP! volume problems

[jackpiazza]

hi there, I've bought 1 month ago a brand new Mark V amp with a 2x12" stiletto's cab

when I set clean channel (gain: h12, Master: h12) and the output knob (with loop fx activated) more than h12 it starts to make noise VERY a loud!! like a thin and crazy whistle, even with my guitar unplugged

when I control volume only by channel (so whit loop fx switch off), no problem, i can crank it all the way up and have MORE volume without any issues.

I'm scared about tubes... what do you think is the problem?


sorry for my english, I hope to have been clear.

Sal


p.s.
when I use the fx loop on, to use the output konb for the overall volume, I tryed also to link send&return with just 1 cable, bypassing all my pedals but the problem still remains

 

[Barry]

that sounds like a microphonic preamp tube . You need to replace them one at a time with a tube you know is good until you find the culprit

 

[HeadlessAxeman]

You sure you don't have microphonic pre-amp problems in your V1 or earlier stages?

 

[jackpiazza]

ok I have red the owner's manual about tube failure, and i think my problem as you said is about microphonic preamp tube, maybe the V6b (Effects return stage) since it squeal only when the fx loop is activated and I increase the output knob wich controls also the Effects return volume... does make sense?

 

[Chester]

try it and see - you could be onto something

 

[jackpiazza]

I did some tests this morning and i discovered that this problem is present only on channel 1, with the loop FX on.
When the FX loop is switched off, if i put master knob of channel one all the way up, doesn't squeal, but i can ear some strange noise or "bump" changing...


Can you tell me (if you know it) how to verify preamp tubes? I know that i have to tap on the glass and earing something strange, but from the back of the chassis I can't controll them because power tubes come first. Do I have open front chassis? how?

 

[Authorized Boogie]

Hi JackP -

Have you made any headway on this subject with your Mark V?

It's possible that this could be preamp tube related but I would also be curious about all the settings/modes involved. Extreme settings (that you would never use when playing) on some Boogie amps could sometimes produce what you're experiencing.

Let us know if you've gotten this taken care of and we can discuss some further options for troubleshooting and getting this cleared up.

Boogie

 

[jackpiazza]

Hi JackP -

Have you made any headway on this subject with your Mark V?

It's possible that this could be preamp tube related but I would also be curious about all the settings/modes involved. Extreme settings (that you would never use when playing) on some Boogie amps could sometimes produce what you're experiencing.

Let us know if you've gotten this taken care of and we can discuss some further options for troubleshooting and getting this cleared up.

Boogie

Hi,
as I wrote in other threads here we are:

guitar and all pedals unplugged:

1) - channel 1, mode clean 90W (bold on)
- EQ and gain flat (h12:00),
- Loop ON
- Master h12:00
- Master from 13:30 to max

2) - same as above but:
- Master h15:00
- Ouput h11:00 or above

Mine's squeals even with gain rolled completely off... but I can put all controls at MAX with channel 2 and 3 and no problems

I can't balance volume between channels or my clean starts to squeal...can't even use boost volume for my solos :\

I sent my amp to the italian's assistance...but they doesn't seem very reliable... so I called mesa in US who said they will do all is possible to resolve this problem...does nobody though about microphonic pre-amp tube??