McIntosh Tube Amp will not come on.

If you have another like preamp level tube, swap it one at a time and hopefully it will root out the bad tube and go to ready state

Try resetting the amp. Instructions should be in the owners manual. 

Are all of the filaments in the tubes glowing? It may not be completing the warm up because of a bad tube.

Agree.  Probably just a bad tube if problems exists after resetting the unit .

I would call up McIntosh, parts department, and plead for a set of new smaller tubes.  See if they can send it out to you without asking you to follow through on all the warranty BS you gotta go through.  Had a problem with small tubes and one was bad and it solved all my problems.  

Some pretty ghoulish stories of their newer equipment not working with remote, slow repair service.

They picked up the phone on the second ring when I needed tech support.  They were super helpful.    Definitely call them 

I've had a MA352 for three years without any issues.  I have called McIntosh support for questions and they were very helpful and responsive.  You'll speak with a tech not a call center front person.

Same. Mcintosh picked up every call unlike nearly almost every other manufacturer I called.

One more thought; try doing a factory reset.  You'll lose custom settings but that may do the trick.

I had a similar problem, I held the power button down for too long which caused the tubes to keep glowing orange.
I had a technician at my home in Brooklyn within two days to take care of it.
Call MacIntosh!

Yes Call McIntosh...they will help you.