help for recovering mesa 400+ bias mod schematics

[berserk84]

Hi everyone, I need some help finding the bias modification schematics for the Mesa 400+. I found them here on this forum a while ago, but now I can't find them anymore. Can anyone help me?

 

[Element Zero]

Paging @agedhorse

Any insight to help point them in the right direction?

 

[agedhorse]

Paging @agedhorse

Any insight to help point them in the right direction?

Nope, I don't have any support documentation for this. It may be long gone.

 

[anderbass]

Not any schematics, but here's an old thread with info/pics my amp tech posted about installing adjustable bias on my 400+:

P

Thread 'Instructions for adding a bias system for a Mesa 400+'

Jun 14, 2009

Hi all you great Bass players out there,
I need some instructions on adding a double bias system in a Mesa 400+ Bass amp. I have years of tube electronic knowledge, but a little help is never a bad thing. I have found a picture of one already done, but it's not a real how to or diy. So if any of the electronic wizards out there can help me out I'd really appreciate it very much.
Thanks in advance from a new member, PMR

• PMR
• Replies: 12
• Forum: Amps and Cabs [BG]

 

[anderbass]

Might be some bias info in this old thread too:

https://www.talkbass.com/threads/i-have-joined-the-dark-side-well-not-really.387202/

 

[agedhorse]

One issue with winging mods without understanding the potential negative impacts is that sometimes unintentional damage happens with really bad results. When we get these amps in for repair, we usually remove all unauthorized mods which ironically usually solves the problem the amp came in for.

Beware of installing any mods, it becomes much harder (and more expensive) to repair when things go wrong.

I don't know if we are still repairing these at the factory, they are very costly and inconvenient to ship.