Question about changing power amp tubes

[BCy2k]

Hi Everybody -

I have 2 pairs of matched Mesa 6L6 STR 440 tubes I want to put into my Mesa 50/50. I've never done one of these before and my question is: Should each matched pair go on the same channel? In other words matched pair 1 to channel A and matched pair 2 to channel B? Thanks.

 - BC

[KD]

BC, I looked up the 50/50, the 20/20 and the 2:Fifty and none of them addressed tube placement per channel (of course they are assuming you're buying MESA matched tubes). The amps are all fixed bias and one manual said the tubes don't have to be matched but there is a loss of efficiency if the bias circuit has to compensate for a mismatch. I would assume since its two power amps, each matched set would go in each channel A & B.

http://www.mesaboogie.com/manuals/2-Fifty.pdf
http://www.mesaboogie.com/manuals/20-20%20Manual.pdf
http://www.mesaboogie.com/manuals/50-50%20Stereo.pdf

[Mongo]

If the tubes are from the same batch they are probably all matched. Mesa is real good about setting a standard and marking all of the ones within it. All 4 of my 6L6's in my MKIV have a painted yellow dot on the base.

Do yours have any markings?

[BCy2k]

Thanks for the help KD & Mongo.

Mine don't have any color coded dots on them. I've got an email in to Mesa but I think Monday is the earliest I will hear from them. they all have the abbreviation "GRN" on the base. I was wondering if that may be something.

I bought these from a guy on ebay who stated he took these out of his brand new 'out of the box' Mesa amp. He put something else in there right away - supposedly these have zero hours on them.

Seems like Mesa tries to make this pretty adult/idiot proof. They came to me boxed in pairs, so I'm guessing of I put one set in channel A and the other in B I'll probably be okay.

[Mongo]

I expect you will be fine.

Putting one set in each channel is the best bet. If there are no obvious marking differences between the tubes, they are probably from the same batch. I've never known Mesa to send out a new amp with anything but completely matched tubes. My experience is limited, but consistent...

[BCy2k]

Whaddaya know - I got a reply from Mesa on a Saturday - it's as we suspected - keep the matched pairs together, one pair on channel A & the other pair on channel B. Since they're all probably from the same batch it probably wouldn't matter all that much anyway.

[Mongo]

New tubes in a Mesa, just gives you a nice warm feeling inside....   

Cool that they replied on a Saturday.