Valve positions in Dual Caliber Studio 20

hello everyone, I am extremely new here and this is my first post, Please be gentle with me :?
Please help if you can, and direct me to the proper place on this board if thats necessary. I haven't made any searches yet !

I just got an old Studio Caliber 20 amp, the one without the graphic eq and am looking to replace the valves, which I will do this week.
there are 6 12AX7s and 2 EL84s
can someone tell me please, which valve position is which on the pre amp section, there is a mullard 12AX7 in amongst the mesa valves, its the 3rd one along from the left. I'm looking to do a full replace (maybe keep the mullard) but would like to know which one is the Phase inverter, which valve is involved with the reverb, which is for the 'lead' channel gain etc, anything would be appreciated. I've seen a picture of the inside of this amp on the Unofficial Warmoth forum, so I kind of know which is V1, but what does each valve do?

I'm ok with the EL84s I just replaced those with a matched pair of Tung sols but i have a pair of ancient unused Brimar's that I might try out.

also, i don't know how old this amp is, any pointers on that? just a ballpark figure of when these amps were made.
I can't get any pictures up here yet as I'm a bit rubbish at stuff like that.

cheers,
Tango

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this is for the dc 10 as you can see wih the 4 6l6 but the preamp section is the same.

Marvellous, many thanks for the reply.