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MC275...time for new KT88s

chuckworkb said:
Of the three 12AX7's I think the first one is used on the unbalanced inputs only, balanced connections don't use that tube. Is that correct?
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I looked at the schematic for an earlier version of the amp (don't have one for mkVI) and it gave me the impression that the first 12AX7 is indeed bypassed for a balanced input. So I asked this question here http://audiokarma.org/forums/index.php?threads/mc275-mkvi-tube-identification.529653/#post-8655282 and RonC replied that all tubes are always in the signal path, balanced or unbalanced. He would know, so I probably didn't interpret the schematic right.
 
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I have a one slight rebuttal in regards to tubes:

I have seen more than one reply of "just use what McIntosh put in there" and I can certainly see where you are coming from. You are assuming - I think - they must have tried lots of tubes and picked the ones that come with the amp because they are the best from a price/sound/reliability/etc standpoint. While that may be true (I have no knowledge of the process used) I would instead use the turntable analogy.

Turntable makers often include a cartridge with their offering so that the end user can get going immediately. But is it the best ? Of course not. You are free down the road to replace it with whatever you like (that works with the arm and your pre). I am taking the same tack here; that there may indeed be a "better" tube for the 275 because - like any company - McIntosh had to meet a price point and using more expensive tubes would directly affect the street price of the amp.

I'm taking one for the team here and trying to find out if these Psvanes are indeed an "upgrade", or more of a "lateral". And I offer no disrespect or disagreement with those who choose to "keep it stock" (which is ironically my take in the auto hobby). It would have been the safe choice. But where's the fun in that ? :-)

jblnut
 
jblnut said:
...

I'm taking one for the team here and trying to find out if these Psvanes are indeed an "upgrade", or more of a "lateral". And I offer no disrespect or disagreement with those who choose to "keep it stock" (which is ironically my take in the auto hobby). It would have been the safe choice. But where's the fun in that ? :)

jblnut
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Interested to hear what your thoughts are after you've given them some time. Will you leave the small signal tubes as is? Could color your impressions if you change them.
 
I'm using 6550 Gold Lyon reissues in my vintage rebuilt 275.I have vintage Amperex orange globe & vintage RCAs for the other tube positions.I have no complaints about the way the 275 sounds!
 
drillher said:
I'm using 6550 Gold Lyon reissues in my vintage rebuilt 275.I have vintage Amperex orange globe & vintage RCAs for the other tube positions.I have no complaints about the way the 275 sounds!
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Same Amperex 12AX7 orange globe here, great tube for MC75, better than stock tube in musicality without scarifies
 
Seamaster said:
I disagree with others that McIntosh "voiced" their amp with stock tubes without testing other options, it is a business decision I think.
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Of course it is a business decision and I don't think anyone alleged that they did not try other tubes. But it stands to reason that they would try their darnedest to make the amp sound good with the tubes they were distributing it with. Wouldn't you if you were them? After all, that is how people hear the amp at the time they are making the purchase decision.

For the record, I am not against tube rolling. I roll tubes in my gear frequently. Some of my gear went from (to me) unlistenable to fantastic when stock tubes were replaced. How tubes are going to sound to your ears in your particular system and room configuration is pretty much impossible to predict in advance. Asking others in a forum may just as likely help you as it may mislead you. All I said that after trying a few other tubes in both the power and signal positions in the MC275, I always found the alternatives either very similar or worse than the OEMs to my ears and in my system. You may come to a radically different conclusion. There is no other way to find out for sure than to try it for yourself.
 
I think you're overthinking it a bit. There are only so many current sources so its slim picking to begin with. That said whoever supplies them is meeting a MC spec or Mac is vetting in house (i tend to doubt the latter but who knows). Any tube with a kt88 designation is supposed to meet a defined specification. Mac also tended to not push tubes to their limits where differences in design might show through. As others said the small tubes would likely make a greater difference in sound. Honestly never had a 275. The front end of my 60s is the same driver as the early 75 variants. I haven't heard much difference rolling small tubes . (I've owned other gear (not Mac) that made a great deal of difference rolling front end. I was trying to play with the voicing on my CE C22 a while back and reached out to Roger Russel. He basically said any tube performing up to spec would sound right. I am a believer in sonic differences of different brands (types) of tubes though i think certain designs are more resistant to differences (i feel better designs)(which is where i think Mac falls squarely (designed so tubes don't make or make very little difference)). Therefore you can chase the nth of sound (and we all do so i won't fault your efforts). I also think you have to decide for yourself which is right. Feel free. All the people that sell, build , restore, service Mc gear never say " you really should use these for best result" There must be a reason.
 
Each MC275 is bench tested as part of the production process. It must meet all specifications with the new tubes installed. If a tube does not allow the amp to meet specs it is rejected as this is the way we have always built amps.

Thanks,
Ron-C
 
Ron,
Just so it's clear, I always assumed the amps were tested and made spec before leaving factory. I just assumed (Mac being a bigger buyer than most for current production tubes probably put out to bid for tubes labelled McIntosh meeting a certain spec. Whoever won the bid would cull the production after testing before shipment to Mac. I tended to think Mac would just make sure amp made spec after assembly and not further test tubes before installing. If supplier had a high failure rate it would probably result in Mac sourcing from someplace else.
I have no first-hand knowledge of this process. This just seems to make sense for everyone.:idea:
 
nj pheonix said:
Ron,
Just so it's clear, I always assumed the amps were tested and made spec before leaving factory. I just assumed (Mac being a bigger buyer than most for current production tubes probably put out to bid for tubes labelled McIntosh meeting a certain spec. Whoever won the bid would cull the production after testing before shipment to Mac. I tended to think Mac would just make sure amp made spec after assembly and not further test tubes before installing. If supplier had a high failure rate it would probably result in Mac sourcing from someplace else.
I have no first-hand knowledge of this process. This just seems to make sense for everyone.:idea:
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The best way to check tube quality is when it is installed in the amp or preamp under test. This is no different than a transistor product. If an installed tube keeps the amp from making spec then it is rejected. This fall out rate has been something that has always happened including much heralded brands like GEC KT88s and Telefunken tubes from the golden era. McIntosh has an experience data base to judge quality.
Most folks don't have a test bench and rely on tube testers or opinion which is understandable. Installed dynamic testing is the final word on tube performance.
Ron-C
 
Disappointment...thy name is Grant Fidelity...

Having read the thread from a few years ago about the earlier version of these tubes pulling too much current and blowing fuses on the 275, I was crystal clear about this when I ordered mine. Rachael seemed to know what I was talking about and asked for a few extra days to put together a 'low emission' quad set. They arrived today and I just got done removing them from the amp, as well as installing a new main fuse. Less than a minute after power up I got a loud 'bang' followed by silence. Grrr.....

Very, very disappointed here.....tried to head this off at the pass but clearly, I was unsuccessful.

jblnut
 
I don't think so...amp seems to be working ok as far as i can hear. Would it still be working with a blown resistor?

jblnut
 
Nope. You are probably fine. The Genalex Reissues took out the resistors in my case, so I was curious. Will you request another set, or a refund? Hope it works out for you.
 
Probably refund...waiting to hear back from them now....

My Genalex set lasted just over 4 years...not sure which direction I will go now.

jblnut
 
Someone once told me you should expect 3000 or so hours on output tubes. I think 10000 or so on small signal tubes (I know there are no hard and fast rules and i wouldn't be surprised if many do better (or worse). My point though , 4 years may not be an unusual life depending on usage. (One of the reasons i can't imagine running NOS unobtanium output tubes). You can see what Mac suggests (sells) i don't think you could go wrong. You could reach out to someone like Jim McShane (small, honest guy, who'll take the time to listen and recommend based on his experience)
(no affiliation). You could listen to us bicker and suggest:biggrin:.
 
I contacted Jim McShane and will be doing another 4+ years with the Genalex GL reissues. They were good enough for the last 4 years and my hearing isn't getting any better...LOL. Too bad about the Psvanes. If nothing else, they are damn cool looking tube. Reminds me of my favorite line from Gumball Rally:

(trying to get the E-type to start so it can enter the race)

Man 1 - "It's an elegant design"

Man 2 - "I wish it ran"

jblnut
 
Jim rocks. Two days later I have new GL's in there plus four NOS Tele 12AT7s, for less cost than the Psvane output tubes alone. Sound is slightly more mid focused now (which is what I wanted) with a little less output at the extreme low and high ends of the spectrum. Very pleased with the results and I would highly recommend Jim to anyone.

jblnut
 
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