Various questions from a new Mark V 1x12 combo owner

[laxulus]

I've recently bought a used Mesa Mark V:90 1x12 combo and have a bunch of questions.

Tubes

1. How should power tube changes be done?
   1. Can I swap the inner and outer pair separately as matched pairs, or do I need a matched quad?
   2. I have an old single matched pair of SED "Winged C" 6L6 tubes. Can I plug those into the inner or outer slots on the Mesa without issue, even though they aren't "Mesa spec" tubes? I'm just interested in using them in something, as either backups or to possibly make the amp sound better/different.
   3. I know some sites sell "Mesa spec" tubes, but I'm not American so buying from those sites is expensive. Are the Mesa tube specs listed somewhere so I could go to my local tube vendors and ask for the right stuff?
2. What's the easiest way to swap preamp tubes on this thing? It looks like it might be just removing the power tubes/rectifier and reaching in to get to the preamp tubes. I have no idea what is in it atm, but I'd like to play around with my old stash of preamp tubes (Svetlana/SED 12AX7, JAN/GE 5751, various JJs, GTs and more)

Age

How do I figure out how old my amp is?

I haven't really looked much under the chassis for any markings or serial number, but it's possible they have worn off.
The previous owner did not know much about the history of the amp.

Have there been any circuit changes over the years? In case something like that comes up if I have to get it serviced.

Speakers

Any recommendations for speaker swaps specifically in the combo?

It has a MC90 in it that seems to work just fine, but I'm not sure it's my favorite. I much prefer the sound of the amp through my 4x10 with 10" Greenbacks. Yeah I know, open back 1x12 vs 4x10 closed back is a totally different thing before even talking about the speaker differences.

I find the MC90 sounds nice for cleans and low gain, but the higher the gain goes the more I seem to struggle with treble and excessive mids with it. It's a complex amp to learn to dial in of course, but I find that on the GEQ I am either keeping the 2200 and 6600 Hz sliders flat or reducing them to combat that when using it as a combo.

I don't really care for V30s too much, and I'd prefer something that can handle the full 90W even though I'm not likely to ever run it at those ungodly loud volumes.

 

[Quiffmiester]

Congrats on your new acquisition!

I'd wait for someone to confirm all of this, but I believe the inner/outer pairs can be matched without needing a matching quad. Mesa spec tubes are available in non-mesa branded guise - I have a backup set of JJs for my V:25 and are using JJs in my mark IV. If you're in the UK, check out hotrox for sets. Whatever tubes you use, they will need to be 'in spec' so putting random 6L6s in might mess things up a bit. I have no idea what determines them as 'in spec' so can't suggest what you could measure if you wanted to explore using the SEDs.

I'm not a speaker aficionado, but I love the EVM12L with my mark III/IV. Heavy though. My mark V is the mini one so has a 10" creamback rather than the MC90, but I have a 1x12 cab with the MC90 in it and I much prefer the EVM12L. R.e. sliders - I wouldn't worry where they end up so long as you can get the sound you want out of it. I find my ears and the room I'm playing in change so settings that work fine at one volume at home may be completely different to those in a pub. Sometimes I'll keep them both flat, or drop the 6600 lower - this is with a different version of the mark V, so I'd be surprised if it's the speaker that's doing this for you. Also, initially I Geq'd for all channels but recently I've turned to just using it for high gain channels and turning it off for clean/slightly dirty sounds. Might make a difference if you haven't tried it that way.