Hi all. I recently purchased a used MC275 in very good condition. The original owner said he had it service not too long ago. The amp appears to work fine but the tubes are very dim. I had them tested and they are fine with about 1/2 life still on them. Not sure what to do. Do I need new tubes or is there an adjustment I need to make? If I need new tubes then could someone give me an idea what to get and where to place them on the amp (which slots)? I want quality tubes so please, ANY guidance would be appreciated. Thank you
The “brightness” of the tubes does not reflect on thier function. The “plate” can surround most of the cathode on most and obstruct the visual light to a great degree. If the actual plate, which is what you predominately see on the power tubes, starts to “glow” (red plate) turn the amp off immediately and have the bias checked. The small signal tubes also will only have a small amount of visual light present. More glow noted in a fully dark room, but again does not relat to function.
Are you refering to the Green LEDs? Or the tubes themselves? the LEDs on that amp are actually nice they will turn colors when the tubes are getting weaker and need to be replaced. Red for an issues, amber at start up and green when everything is good. would this be the lights you are talking about?
I own the mc275 vi version and love it. Mine has the LED tube indicators, but I don’t believe yours does. Ron Cornelius at Mcintosh told me that on average the 275 tubes last between 5,000-10,000 hours...so if you like the sounds of the tubes you have, they should still have lots of life.
As as far as tubes, I’ve swapped out a few tubes. I really like the golden lion kt-88, they seem to have more body and bass. I tried the newer tung-sols in the 12ax7 spots, but didn’t care for them. They sound thin. My current setup (that I like the best so far), 1 Golden lion 12ax7 inverter spot, with 2 RCA 12ax7 followed by rca blackplates 12at7. However, everyone’s ears and stereo is different. Good luck!
I'm a proud owner of a Mc 275 mk3,my tubes are not bright or lite up like other tube amps I've owned so I think theres a pattern here,however never an issue and love the sound,of course my kt 88s are Black Treasures so you can't see them well any how,but the 12 ax7 s don't burn bright either, wouldn't be concerned!
If you really want to see the tubes glow, you can turn up your preamp as loud as it can go, and the power tubes do tend to glow a little brighter.
Seriously though, there are many amps and preamp out there that the tubes barely glow. I have a Berning TF-10 that you can barely tell the tubes are on. Tube brightness is no indication if they are "good" or not.
2112oracle: Have you tried any other KT-88's? I was curious about the black treasures, but the cost at the time was a little steep for me.
I concur with the assessment made regarding the dimness of the tubes not being an indicator on their performance. I know it can be confusing with all of the Tube Amp Porn Photos on the internet revealing as much light as a fireplace on each Amp. - Marketing
But most important is how they sound to you. If you do not like how they sound, then I suggest swapping out the Tubes. I have gotten some fantastic stuff from this site.
the MC275 IV is one of the very best amps ever. I have heard much more expensive amps that cannot touch it for musicality. A true gem and is very well made, many of the transformers for this amp were wound by the same person who wound the original MC275's. I almost never see these come up for sale and for good reason, they are magical. one of the great amplifiers in the history of audio. Enjoy my friend. The new ones are not as good and the metals used in newer models are inferior to the lead solders in this amp.
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