Get a second opinion but in theory I think that's ok: I'm no expert but my understanding is that as long as the ohms load on the speaker isn't less than the output on the amp you don’t damage the output stage of the amp. 4 ohm output into an 8 ohm speaker is fine as far as I understand it.
However, someone way cleverer than me needs to clarify whether or not it’s safe to use both the amp’s speaker outputs at the same time.
Its been a while since I learned this stuff but I thnk if the amp is perfectly matched with a single 4 or 8 ohm speaker in the appropriate output then using both at the same time will result in a mismatch (reflect back a combined lower load to the primary winding of the OP transformer) and cause more power to be dissipated in the output tubes - potentially reducing the life of the tubes.
Help !!! Im ashamed that I do not know this stuff, but it is what it is, and I dont want to hurt my new equipment.
My MB TA15 has a 4 ohm and a 9 ohm out jack. My new REC series MB 2 x 12 Cab (that was a floor model and did not come with a manual)
has two input jacks......one for 4 and one for 8. From reading on here, I understand I can do the 8 ohm out on the amp to the
4 ohm in on the cab and it will sound different, but no harm will come to my equipment. So I guess its also ok to do a 4 out on the amp into
the 4 in on the amp, but never a 4 out on amp into the 8 in on cab.
WHat are the differences I will experience in sound when I do any of the above and what is safe and the recommended ?? I have only done the 8 out and 8 in so far.
Thank you for your help and info!!!