Mesa's have a lot of tubes (I have a Lonestar Special), I wouldn't replace them all unless you have to. You need to follow skeksis's advice and read the manual, it is pretty helpful. You can also get the schematic at:
http://www.schematicheaven.com/boogi...ogie_22cal.pdf
First check out Joe-Bob's suggestion, you've left the heaters on all week so maybe one of the wires burned out (the heaters are basically cathode toasters). If one did the orange glow will be missing.
Since your reverb is working the power tubes and V4 (reverb driver and recovery) are working. Also the phase inverter V5 should be fine.
Your lead channel is the only one that uses V1, if the rhythm channel works it it probably V1.
Both channels use V2, but the rhythm uses both halves, one for its input preamp. The both channels used the other half as a preamp stage. So if only the rhythm is dead its probably V2.
If both channels are dead its either V2 or V3, and if they both glow its a crap shot, try one at a time, then both.
Dang I should type faster! you replied while I was writing!