Class A impedance question is this safe for my amp

[MrMarkIII]

If you are talking about the Mark III, the answer is: no, you do not need to alter anything to run in "Class A".
But running out of the 4 ohm speaker jack will yield a smaller, more compressed sound with less presence.
Flip that switch, crank that Master, and RAWK!

 

[MrMarkIII]

If you are talking about the Mark III, the answer is: no, you do not need to alter anything to run in "Class A".
But running out of the 4 ohm speaker jack will yield a smaller, more compressed sound with less presence.
Flip that switch, crank that Master, and RAWK!

Its a MK IIC+ does that make any difference

No.

 

[stokes]

Switching from 4 tubes to 2 tubes in any amp will cause an impedance mismatch,but the OT in a Mesa amp can handle it.Most amps can handle 100% mismatch in either direction,Marshall being an exception,I dont recommend doing it with a Marshall amp,the older ones anyway.If you have an amp that needs an 8ohm speaker you can go with a 4 or 16 ohm speaker,the 16 ohm being the safer choice.A 4 ohm speaker in this case will cause the power tubes to run a bit hotter.Mesa amps are biased so cold,it wouldnt really matter.