weird sound with a mark IV

[K-Roll]

hey guys, I just thought you might have some ideas what to look at..
a month ago, I took my old mark 4 version A to a tech who did a cap job (filter caps + eq+bias caps) and who set the bias using a new quad of SED =C= 6L6s tubes and the issue is -

when I play on usual rehearsal volume on the lead channel and I do some palm mutes/ staccatos I hear weird noises which remind me of small ceramic plates, teacups and spoons resonating on a table when you smash it pretty hard with your fist you know.. those resonating weird buzzes.. and i can definitely tell that the distorted channel does not sound quite ok as if that resonating stuff was present even in the sound comming out while playing and sounds rather worse..
i can hear it on the Ch2 as well when I play some stuff on the upper 7th B string it sounds glassy and has a 'ceramic squeak' to it.. i can't describe it better

I tried swapping all preamp tubes with 5 brand new (v1 tung sol and the rest JJs) tubes but it did not make any difference

i could just drive to the tech and let him have a look at it again, but it's quite a ride from where i live and I wanted a 3rd person opinion on what to look at especially with old boogies
thx for any ideas, i am getting quite desperate

 

[swbo101]

I've never heard anything like that before. Do you also hear it in the R1 clean channel? If so maybe there's an issue with the new power tubes you put in? Not sure. The only question I really have is why did the tech re-set the bias? Mesa amps have a fixed bias, I'm not sure if that's something you want to have done to these amps. Generally you buy tubes that will fall within a certain tolerance range for these amps. Unless of course you specially asked for him to do this.

Did you ever hear that sound before the cap job?

 

[swbo101]

Another question....are you confusing these ceramic plate sounds with some type of microphonics?

 

[K-Roll]

the tech set the bias according to the new set of tubes, from what I remember, that weird 'breaking' noise was present even with older power tubes but in lesser amout, it sounds as if the tubes were resonating and this resonation was being transferred into the sound whilst playing on the lead channel (which causes the most movement of the cab while playing on gig volumes)

and one more thing i realized was that yesterday I tried using a delay in the loop but even with the delay being off and the loop off with cables being stuck in send and return of the amp, the amp started picking up feedback starting with low volume and increasing even with my guitar being muted .. seems like something is pretty ****** up :roll:

 

[boogiemon]

sounds like you need a new tech.

 

[dodger916]

the tech set the bias according to the new set of tubes, from what I remember, that weird 'breaking' noise was present even with older power tubes but in lesser amout, it sounds as if the tubes were resonating and this resonation was being transferred into the sound whilst playing on the lead channel (which causes the most movement of the cab while playing on gig volumes)

and one more thing i realized was that yesterday I tried using a delay in the loop but even with the delay being off and the loop off with cables being stuck in send and return of the amp, the amp started picking up feedback starting with low volume and increasing even with my guitar being muted .. seems like something is pretty f%&# up :roll:

Couple of things. First do you know how he set the bias? As swbo101 says, the bias is fixed, meaning there is not pot to adjust it. The only way to adjust it is to replace resistors. Did he do that, or did he find tubes that matched the fixed Mesa bias?

I always felt the Lead Channel did not create the most amount of cab vibration, and the cleaner channels put out more low end.

Feedback with volume off or "guitar being muted" suggests a highly microphonic preamp tubes.