andre tchmil

My Mesa dual rectifier sucks, need some help, amp techs !
« on: November 29, 2007, 10:26:29 AM »
My Mesa Boogie Dual rectifier started to output a very weak muddy sound yesterday, with about 50% of the gain it could normally produce.
I replaced EVERY tube in it , no luck.

Any idea where I have to look for?


pucho812

My Mesa dual rectifier sucks, need some help, amp techs !
« Reply #1 on: November 29, 2007, 10:42:35 AM »
Start with the PSU... Check for voltages. Check the rectifiers then move on. Have you tried patching out of each section to see where the problem lies. I currently fixing an Apeg 350 solid state amp for a friend. So far with testing, I can patch directly out of the preamp either using the direct out or pre amp out points and get a nice looking signal. The power amp section is where all the issues start as it has noise as well as it also is screwing the up the built in limiting.

Here is a link to a schematic of a Mesa Boogie Dual rectifier. Not  the offical one from mesa however I think you can get one off their site as well

http://www.freeinfosociety.com/electronics/schemview.php?id=507
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

12afael

My Mesa dual rectifier sucks, need some help, amp techs !
« Reply #2 on: November 29, 2007, 11:30:40 AM »
as pucho say use the loop to know where is the problem.

1 use other power amp and send signal from the send or preamp out of your dual rectifier.

2 use other preamp to drive the return of your dual rectifier.

- if the first test work ok the problem is in the power section.
- if the second test work ok the problem is in the preamp section
- if both test have a bad sound the problem is in the power supply section.

When you have isolated the problem, measure some voltages, check cold solder, mechanical parts, etc.

good luck!
Rafael
heavy metal is the law!!!

Re: My Mesa dual rectifier sucks, need some help, amp techs
« Reply #3 on: December 01, 2007, 08:58:24 AM »
Quote from: "andre tchmil"
My Mesa Boogie Dual rectifier started to output a very weak muddy sound yesterday, with about 50% of the gain it could normally produce.
I replaced EVERY tube in it , no luck.

Any idea where I have to look for?


If you open up your rectifier- it would be great if you could take pics of the PCB so members could work out a correct schematic????

I used a Mesa simu 90 / 90 power amp with an ADA preamp- and all I can say is that it was the DOGS B*LL**KS. :grin:  :wink:

jensenmann

My Mesa dual rectifier sucks, need some help, amp techs !
« Reply #4 on: December 01, 2007, 09:56:34 AM »
the switchingcontacts in the FX-loop-jacks?
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

BYacey

    Where dogs wear thermal underwear, Alberta, Canada
  • Posts: 769
My Mesa dual rectifier sucks, need some help, amp techs !
« Reply #5 on: December 01, 2007, 11:25:19 AM »
I would start at the output tubes, this is where all the heavy action takes place, and the most likely stage to develop problems. Are the B+ voltage on the plates good? If so you can probably disregard looking at the power supply rectifiers. Bias voltage on the output grids where it should be?

If everything above checks out and you have a scope, apply a sine wave signal at the input and check the signal  at the grids of the phase inverter / driver tubes just before the outputs. I'm sure you'll find something here isn't what it should be. It's a pretty simple output circuit and should be easy to troubleshoot.

Looking further at the schematic, I see they have the 5U4s switchable to give  an underinflated beachball sound. I would do all the above testing with the silicon rectifiers switched in first.
Bill Yacey
"Adjust R116 for least smoke"


 

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