Mesa/Boogie Bass 400 (plusless) Help!!!!

[Daionman]

So what´s up guys, this is about my first post.

I have a nice mesa 400 non plus from the 80's
currently with 6l6 tubes,

The question:

Is it really possible to switch to 6550's?

I don't see a bias knob on this thing, is it fixed bias?

Help!!!

 

[Grooveman1961]

Yup, you can run 6550's.

you need to change the resistor that sets the bias, or install adjustable bias.

It is fixed bias. It will be fixed bias even if you put in adjustable bias.

Fire up the googler for more details, but there are two major kinds of bias, Fixed, or Cathode. The terms describe the circuit configuration, not really adjustability.

Call Mesa, they should be able to tell you which resistors they used for the different versions.

 

[Tualatin]

You can just drop the 6550s right in. That's what the amp was designed to run, and that's what it came with out of the box. You shouldn't have to adjust any bias settings albeit fixed, unless whoever put the 6l6's in messed with the resistors, which I doubt. I like JJ tesla's in my Plus.

 

[Daionman]

Nice i´ll check what's the status of my amp...