Mesa studio caliber amp: Hissing, squeeling feedback type sound

DrGonzo

Hi I have just acquired (yesterday) a awesome Mesa Studio .22+ second hand in joburg
Now, when i jam i randomly get this sort of squeel noise out the speaker (not always, in random intervals, sometimes only after about 20 ins of being on)? can be loud or just slighlty in the background

Please help. I am a tube newbie so dont know anything about that stuff....
Could it be the tubes? Could it be something circuit wise
Could it be the speaker?
could it be the power supply from the wall?
could it be from the pickups in my geet?

im confusd. such a awesome sounding amp i really want it to run smoothly...
its wierd i didnt notice it the +-3 times i jammed on it before making decision to get it, as soon as get home, i get this problem...

HELP would be GREATLY appreciated?!!!

ralley

Good buy - I've had the same amp for 20 years now.

Your problem sounds like a bad preamp tube or a failing capacitor.

You can test for a bad tube if you are VERY CAREFUL - unclip the metal plate that serves as a tube protector and let it drop down out of the way (it will hang there). Allow the amp to warm up on standby and then switch it on. Now being very careful not to touch anything, tap the tubes lightly with something non-conductive (a chop stick works well).

You are looking for a tube that makes noises when you tap it. Looking at the amp from the back the tubes left to right are V1, V2, V3, V4 and V5 followed by the (bigger) power tubes. Your problem is probably either V1, V2 or V3. If you find one of these is noisy (microphonic) try swapping with V5. V5 is used in the reverb circuit so gets less use and is less likely to fail.

If you do need new tubes the JJ ones from Wim's (wife) aka mrvalve work well.

A safety tip when poking around in the back of a live amp - keep one hand behind your back, if you do touch something live the current won't cross your body through your heart.

If it needs a capacitor replaced then thats probably a job for a tech but its a quick, cheap fix.

So far in twenty years mine has only needed a set of tubes, a cap job and a pot cleaning. Boogies are made very well and rarely give problems. The guy who did my cap job had never had to do one on a Boogie and he's been the main amp tech in Auckland for years (his workshop is like Aladins cave!).

Rob.

Gearhead

+1 but be very careful indeed with opening tube amps. Unlike transistor equipment, the voltages inside are huge and there's lots of stored energy. If you want to touch anything, first switch the amp off, unplug the power lead and leave it alone for 10 minutes.

It would also make sense to buy 3 to 5 12AX7's and to just change the tubes that are in (in the order described). That way, you have spares and will probably not need any of them for quite some time.

ralley

Gearhead wrote: +1 but be very careful indeed with opening tube amps. Unlike transistor equipment, the voltages inside are huge and there's lots of stored energy. If you want to touch anything, first switch the amp off, unplug the power lead and leave it alone for 10 minutes.

Sorry but this is VERY dangerous advice - leaving a tube amp switched off for 10 minutes will NOT discharge the caps. Poking around inside can then be fatal. If you are working inside discharge your caps properly and keep them discharged. Checking the valves is not too bad if you are careful - going inside the chasis can be a whole other realm.

Rob.

Gearhead

ralley wrote: leaving a tube amp switched off for 10 minutes will NOT discharge the caps

The Studio .22 will discharge through the rectifier diodes imho. I should have mentioned you must switch the standby switch on.

Edit: if you switch off the standby with the mains on, the heaters of this amp will remain powered. This means that the HV caps will drain through the tubes in less than a minute.

We agree that tube amps should be left alone unless one knows what one's doing. That's in fact why I suggested to just roll the tubes and leave the fault finding.

DrGonzo

Thanksmucho for the advice but i seem to have found the problem..

As i said, i only noticed it when i got home (otherwise i wouldnt of bought it obviously!)
so i took it to a friends house( actually 3 different houses to double check) and no problem watsoever..

So can it be safe to conclude that it is the wiring/earthing whatever in my room / house ??( i stay in a really old student commune, had loads of electrical related probs before).

Is it dangerous for the amp to be played through such a dodgy electric current - i assume it is...
but i want to be able to jam my own amp in my own house as well!!! if its not ill just get a noise gate or something to block it out...

Gearhead

Get it to a tech - it really should work with less than perfect power. The earth might be faulty, tell it to the guy who is to repair the unit. There's tube guru's on the forum from Gauteng and from Cape, so you can get it sorted right here ?

cain

Dude, if you ever see another one around, send me a PM, i would love one of those!

DrGonzo

Gearhead wrote: Get it to a tech - it really should work with less than perfect power. The earth might be faulty, tell it to the guy who is to repair the unit. There's tube guru's on the forum from Gauteng and from Cape, so you can get it sorted right here ?

thanks again dude for your advice. im really certain tho, that it is the wiring in the house or the power points in my room because when i play it at other peoples houses, it works 100%...
thats crap, i cant even jam my own amp in my own house!!!

DrGonzo

Francis Viviers wrote: Dude, if you ever see another one around, send me a PM, i would love one of those!

will do man. Yeah i am so stoked i got one of these. my dream to own a mesa boogie came true in a relative short time, i thought it would be years before i could afford one! lucky i found one second hand for a realtively cheap price.
I have never read a bad review about the studio caliber so i had to get one. at first i though 22 watts would be too little but holy crap this amp is LOUD!

Keep looking around junk mail and gumtree. not too long ago there was a guy selling a ORIGINAL mark 1 head for like 7K (there was only a handful of those ever made)...

cain

Allot of people make the mistake by judging the wattage. A 22 watt valve amp does NOT sound the same as a 22 watt transistor amp. The valve is MUCH MUCH louder. My 120watt valve amp was only cranked half way once in the play room, the roof and walls started vibrating and i cracked one window ... 22 watts is more than enough especially on a 1x12.

On the sound front, look if you cant find something that you can run the power through like a lightning protection unit or something. I dont know if it will work but its worth a shot ...

TomCat

DrGonzo wrote:
Gearhead wrote: Get it to a tech - it really should work with less than perfect power. The earth might be faulty, tell it to the guy who is to repair the unit. There's tube guru's on the forum from Gauteng and from Cape, so you can get it sorted right here ?
thanks again dude for your advice. im really certain tho, that it is the wiring in the house or the power points in my room because when i play it at other peoples houses, it works 100%...
thats crap, i cant even jam my own amp in my own house!!!

Bump....

@ DrGonzo

Did you get sorted out with your amp...??

DrGonzo

TomCat wrote:
Bump....

@ DrGonzo

Did you get sorted out with your amp...??

Yeah man thanks, I got it back today... it turns out it was a tube problem. the preamp tubes (12ax7's) were the stock tubes thus making them over 20 years old. those things were fucked!!
So all tubes were replaced and amp had a general clean-up and maintenance and it is now sounding Orgasmic!!!

TomCat

Cool....Glad to hear you are back and rocking....... ? ?