BIAS mod to an Express?

[MojoFly]

I found this comment on the HC forum. Is this true?
"you CAN bias a Mesa/Boogie. They have it covered up on the board. According to my amp tech, they put some kind of plastic coating or something over the bias pot. So you have to go in and find it, remove the cover and you're good to go."

I'd love to be a to have this ability verified by any techies here.

 

[EtherealWidow]

Can't comment on the guts, but I know that there is in fact a mod that you can do to boogies that will allow you to bias them that will not void the warranty if done by a certified tech.

 

[a2dconverter]

"They have it covered up on the board. According to my amp tech, they put some kind of plastic coating or something over the bias pot"

Hey Mojofly, the guy on HC must have confused Mesa with somebody else...there is no bias pot hidden or covered in a Mesa Amp. You have to replace a resistor on the circuit board with a potentiometer...

The pot can be mounted internally or externally like this...

see here for more pix...

http://forum.grailtone.com/viewtopic.php?f=30&t=36146

I've been using the amp like this for a year now....make sure 'your' tech knows how to do this without destroying your amp.

This modification will void your warranty regardless of who does the mod...including the Mesa Mod Messiah

seeya

Joe

 

[MojoFly]

a2dconverter - Nice work!

The good news is it can be done.
Sadly it may require more modding than I was originally thinking.

I guess the first question would be whether a "tunable" bias mod would really justify the expense.
I mean, as compared to just purchasing some adjusted/metered Power Tubes to be installed in a fixed bias Mesa.
I know Bob a Eurotubes works hard in that arena and suspect Doug's Tube would do the same.

The other thing I'd be interested in is whether any talent here would willing to do mod work for others.

Perhaps there's a resource pool here I haven't found.

Ideally, if I went the mod route, my preferences would be:
1) Tube bias probe housing and adjustment (pot) like above

2) 7 pin midi allowing for power thru the line to controller (Think Rocktron Midimate)
Spoiled by my Triaxis I guess :wink:
I do also recall someone modding their F 50 midi linking it to their G Major

3) If preferance #2 is possible, is the the ability to control Clean, Crunch, Blues, Burn modes, reverb and contour thru midi controller then an option?

I know this may a wishful thinking but, never hurts to ask.

Thanks