More 2:90 questions...

[lowmantotempole]

OK so I finally broke down and bought a used 2:90 power amp.

From what I have found on here I am guessing it is a Version 1. It has the blue light on the front panel and the writing on top, centered above.

I love tube amps but have always had numerous issues with every one I have owned except one (Bad Cat Lynx)... This is mainly due to my lack of knowledge and getting frustrated very easily with my tone.

For preamps I am using the following: ADA MP-1 (original), and a Voodoo modded Marshall JMP-1. So those are a good start.

Last week I noticed my tones were kind of flat and blah sounding. I mean what were supposed to be "classic" Marshall tones on the JMP-1 are really lacking that KERRRRANG sound. They were sound very sharp and lack warmth. I immediately swapped out the JMP-1 tubes with ones I know are good. Same problem. I tried both preamps as well. I've also tried both channels on the 2:90.

So I popped the top of the 2:90 to get a good look at the power tubes. I powered it up and turned off the lights to check them out. I noticed that the tubes for channel A were glowing an orange color. The tubes for channel B were glowing a neon blue color with orange in the middle.

I turned it off, waited for it to cool down and took the tubes out one my one. I wrote down which tubes went where so I could put them back where they were.

First Question: Why are there two different kinds of tubes in there? I mean they are all Mesa
tubes but 4 are labeled green and 4 are labeled red.

Second Question: I see that this is a "fixed bias" power amp. I do not want to mod it to
change the bias. So with that said, do I really have to use Mesa tubes?
I'm guessing NO.

Third Question: How will using other brands of 6L6 or 5881 tubes affect the amp?

Forth Question: What other tube options do I have?

Fifth Question: Since this amp is basically two power amps side by side, can I use different
configurations of tubes for each channel? Like TungSol 6L6 for channel A, and
Tungsol 5881 for channel B?

To lessen the confusion, please state which question you are replying to.

Thanks a TON guys!

 

[MesaGod666]

Hey man,

Welcome to teh Boogie Board. All 2:Ninety tube variations have been addressed and discussed ad nauseum in previous posts. Please use the search feature to read these previous discussions.

To respond to your tube problem with your 290...it sounds like you need a full retube by a qualified Mesa amp tech. I recommend this because you purchased your amp used and you don't know the full history of the amp. You only know what the seller wants you to know. The tech will run diagnostics on the amp checking to see if there is anything else possibly going wrong. I also recommend reading the operating manual for the amp as these amps can be seriously damaged with even the slightest of incompetence.

First Question: Why are there two different kinds of tubes in there? I mean they are all Mesa
tubes but 4 are labeled green and 4 are labeled red.

It's only a problem if you mix red and green together on the same channel.

Second Question: I see that this is a "fixed bias" power amp. I do not want to mod it to
change the bias. So with that said, do I really have to use Mesa tubes?
I'm guessing NO.

Third Question: How will using other brands of 6L6 or 5881 tubes affect the amp?

Forth Question: What other tube options do I have?
Fifth Question: Since this amp is basically two power amps side by side, can I use different
configurations of tubes for each channel? Like TungSol 6L6 for channel A, and
Tungsol 5881 for channel B?

Read this article and scroll down to the 290 section.