McIntosh MC-2301 Tube Replacements

I would test those McIntosh output tubes for emissions. I bet they still have a lot of life left! If so, no need to rush to replace them! Ditto for the 12AT7's.

KT88's vs. 6550's? Six of one, half dozen of the other!

@taxmandme 

You are welcome. In my opinion, there is no substantial information to validate that there are frequent reliability issues with Gold Lion tubes. Of course, tubes in general, are subject to various intermittent problems. Some tubes could start making rushing, whistling , or whooshing sounds. With new tubes, it is important to obtain balanced and matched, and maybe, low noise tested. This will help to provide at least some guarantees that the tubes will perform as expected.

Since your amps are 4 years old, and you don’t know how many hours are on the stock tubes, I would recommend swapping out the power tubes for the Gold Lion KT88s. Not many reports of people putting in 6550s in their 2301, although you can do it, why? The KT88 provides the best overall performance and is a proven performer in the 2301. Some amps do sound better with 6550s, but I am pretty sure that the 2301s sound best with KT88s. The 12AT7s should have some good life on them if the hours are low. 
 

Should you decide to swap all the tubes, then going with GL KT88s, and Genalex Gold Lion 12AT7 tubes are a great match. I do have both the GL KT88 and Genalex GL 12AT7 tubes in use. I tried NOS Mullards, RFTs, Siemens in the 12AT7  position but I felt that worrying about a tube going nuclear made me feel neurotic about listening to music. That feeling can come with almost any tube though, lol. 
 

I did extensive testing of EH, Mullard, and JJ KT88s, all in reserve now. I settled on the Gold Lion last. So, testing in my experience, although costly, led me to the GL KT88s. My experience with the EHs tubes led me to believe that the EHs had more of a up lift in the highs, while the mids seemed to be a little less reverberant, or otherwise stated, more dry sounding in that region. This was years ago in another room and with other speakers so my recollection of those tests might not be accurate today. Also, Shugang and PSVane has some new KT88s that I would not mind experimenting with either. 
 

Of the 32 plus tubes I have used over years, I only had one KT88 fail on me. It was not a blowout either, it was just emitting lower power, in which the amps detected as a tube fault. I have tube testing equipment for large, diode, and preamp tubes and verified that the power tube was not working correctly. I got a replacement from the dealer. Like tires, depending on how much use are on the tubes, if one fails after many hours, it might be time to replace all. This is why having a tube tester is important, especially since you are in a tube hobby. 
 

Lastly, tube wear is based on general usage. How loud, which equals more power, will decrease life span of power tubes. Some say, 1000-2000 hours is a good average. However, circuit design and how much power you are using will influence the lifespan. If you listen at lower levels and don’t play the system often, I would believe that you could have at least 3-5 years of service life with the power tubes. This would be based on about 4-8 hours of weekly use. At 8 hours of weekly use, 384 hours a years, this would be about 1920 hours in 5 years. Your hours of use might be more or less than what I am estimating. Bottom line, you will notice tube wear when the music loses its crispness and becomes more softer sounding. Easy to verify with a tube tester or replace tubes on one amp with newer tubes from the same brand, and have a listen. Generally speaking, preamp tubes have a far longer lifespan than the power tubes, probably 5-8 years is a good estimate. Some people swap all tubes at the same time…I did that once, it gets costly. 
 

Happy listening. The MC2301 amps are built to last a lifetime. Their autoformer quad balanced technology, the only tube amp from McIntosh that has it, assures outstanding musical playback performance. 

All McIntosh tube power amplifiers use the Unity Coupled output circuit (a great description can be found in Bruce Rozenblit’s book “Tube Audio Design”).  This inventive and effective circuit is able to run the output tubes conservatively, giving those tubes longer live so I bet the original Mac output tubes in your amp may be fine. However, the tradeoff (there’s always a tradeoff) is that the driver tubes are run hard.  These are likely the 12AT7s you mentioned.  I would consider replacing those first. Good news is that even though NOS 12AT7s are expensive (guitar amp aficionados gobble them up) an (almost) direct replacement tube is the 12AZ7, the only difference being the 12AZ7 pulls 400ma of filament current while the 12AT7 demands slightly less at 300ma filament current.  NOS 12AZ7s are dirt cheap and common as they were mostly used in televisions, though McIntosh has used them as driver tubes in the past, such as the MC275 Gordon Gow amp, a pair of which I owned for over 20 years. During that time I only needed to replace the KT88s once, but the NOS 12AZ7 drivers needed replacement three times.

I don’t have a Mac, but own several tube amps and gobs of NOS and some new production tubes. My Dennis Had Insipre will run KT-88, 6550, EL34 and 6L6.  The amp came with Gold Lion KT-88s. They are  excellent tube IMO.  Clean, transparent, linear with good balance and a touch warm. Rock solid construction, made in the old Reflector factory in Saratov. 

You should also consider Shuguang Nature series KT-88-T. They take a while to burn in, but offer a touch more bass and detail. NOS Svetlana 6550 are an amazing tube, bass, midrange drive, and seductive. Less transparent but make music come alive, as in sitting in the front row.

I don’t own any new production 12AT7s, all NOS. But I do have a Gold Lion 12AX7 Russian gold pin, that is V1 signal tube in another amp, great tube. Just like the KT-88s, clean, transparent, well balanced. Be sure to get Russian version, they also offer a Chinese version. It’s a bit flat and uninspired. If you want to chase NOS, go with Telefunken or Amperex.