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New MC275 Red Plating Out of the Box

s_alvanip

s_alvanip

New Member
Hi all,

New member here and new owner of my first piece of Mac kit: an MC275 MKVI. I just unboxed the unit, took the tube cage off, and connected the power to my power conditioner (Panamax M5300-PM) to see those tubes light up. Much to my dismay the front 7 tubes lit up amber, then green, then as the 4 rear tubes started warming up the Sentry Monitor kicked on and the left 3 tubes in the front started blinking red.

I disconnected the power to the unit, waited a minute, and reseated all 7 front tubes. This did not resolve the issue, so I repeated the same steps for the rear 4 tubes. Please note that at this time I do not have speakers or a source connected, as I am trying to just test power on.

Do I have bad tubes, a bad unit, or does the unit simply not like having nothing connected to it? If this were the case then why wouldn't the other 3 tubes in front light up as well. Any help is greatly appreciated.

Thanks!
 
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Welcome to AK!
Congrats on a great amp. Yes, it is a no no to not have a load (speakers) connected to a tube amp. I am not a tube expert but I do have a couple of tube amps and they need a load on them from what I have learned over time.
I don't know if the newer MC275 has some sort of protection circuit or not, but I would not turn it back on unless a load was connected to the speaker terminals.
Hope this helps and the amp is ok!:thumbsup:
J.T.
 
Thanks for the warm welcome and quick replies. I saw an unboxing that had the amp powered on with nothing attached, but the clip cut away before long so I'm assuming it was shut off shortly after getting the "all green." Thankfully I shut it off and unplugged it right at the blinking red and hopefully the Sentry Monitor saved my bacon. This is my first tube amp and first go around on doing separates, so I'll wait til I get some cabling in place before firing the amp up. If nothing else I got a chance to inspect the tubes and reseat them after transit. Glad to be on these boards finally. :)
 
Did you get an all green at first and then it went to red?
If this is a new unit, and it does the same thing with speakers attached, I would contact the seller for resolution.
Good luck,
J.T.
 
I have two MC275VI. I have no issues if no speakers connected. I am not saying that won't harm the amp though.
 
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As long as there is no put signal you should have no serious issues. Why don't you swap the tubes showing green with the ones showing red and see what if the coloring follows the tubes or stays in place. If it moves with the tubes then you know you have bad tubes. If the the color stays in place you have a damaged amp. Another thought are your selector switches on the amp firmly in the correct position? Some models have switches some don't.
 
The RED small tubes mean you have a bad tube in the left channel which are the two left KT88s and the three left small tubes. One of these five tubes had failed while being banged around in shipment.
Replace one tube at a time with a new tube until the amp turns on and goes green. The last tube you replace which triggers red protection is the bad tube.

Do not move tubes between channels. The tubes have a 90 day warranty from the factory.

Thanks,
Ron-C
 
Ron's got it right, the LED lighted signal tubes indicate where the bad power tub is. As far as turning on this amp with no input or out put connected will not cause this issue or really hurt it.

The OP has a bad Kt88, maybe two...
 
Could be a bad small tube OR a KT88. that is the way the protection circuit is designed.

Ron-C
 
ron-c said:
The RED small tubes mean you have a bad tube in the left channel which are the two left KT88s and the three left small tubes. One of these five tubes had failed while being banged around in shipment.
Replace one tube at a time with a new tube until the amp turns on and goes green. The last tube you replace which triggers red protection is the bad tube.

Do not move tubes between channels. The tubes have a 90 day warranty from the factory.

Thanks,
Ron-C
Click to expand...

So do I remove all 5 tubes and put in one at a time until I get red, or do I leave the KT88s in and put in the three 12s one at a time? I don't want to harm anything by having too few tubes in that channel. I didn't get around to calling McIntosh today but will do that for sure tomorrow. Thanks so much for the helpful info, and to everyone chiming in with feedback.
 
You change one tube at a time then turn the amp on after each tube change.. If you pull out a KT88 and put a new one in does the amp turn on? If not then reinstall the tube you just took out and try the next KT88. When the amp goes Green and stays on the last tube you changed is the bad tube. I have seen the small tubes trip the protection circuit just as much as a KT88 so you may want to start there.
You need one new KT88, One 12ax7a and one 12at7a.
If you do not have all of the tubes in you will always get a red signal and no turn on. We are looking for Green turn on after Orange warm up.

Thanks,
Ron-C
 
By the way the amp never 'RED PLATES'. The Red signal comes from a tri-color LED under the center of the small tubes which is clear glass.

Ron-C.
 
Thank you for the clarification on that. I do not have any spare tubes to try swapping in, so I have contacted McIntosh to see what they can do. Hopefully we should be able to get this resolved pretty quickly. I'll use the extra downtime to source some decent cables and get everything wired in.
 
I purchased it from Magnolia AV on 04/21. Have some cables on order so that I can do a bit more testing without risking anything.
 
I will swing by there this weekend after I get my speakers connected and narrow it down to the potential KT88 that might be out.
 
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