Forgot to mention the obvious.
The two OTs used for the Twin Coupled design give you twice the power output capability xfmr wise. So two standard 100 Watt OTs will make for a 200 Watt resultant.
I would say that Twin Coupled is actually a bargain at the 200 Watt output level, since the OT BW performance is greatly increased as well. (the cross coupled caps between the corresponding primary taps on the two OTs perform the same function as the bifilar winding does in the MAC OT, fixing the class B inductive ringing, again, not really a big deal for audio in class AB) The Twin Coupled design is not just a hack job copy of the MAC as some may often think. It's damn close to exact duplication. Of course, the final results will depend on the front end tube circuit design greatly too. And the driver stage has to handle 50% CFB drive levels still. Getting the effective OT primary Z down using high current tubes will reduce the Vac drive requirements for CFB. TV Sweeps for sure.
The two OTs used for the Twin Coupled design give you twice the power output capability xfmr wise. So two standard 100 Watt OTs will make for a 200 Watt resultant.
I would say that Twin Coupled is actually a bargain at the 200 Watt output level, since the OT BW performance is greatly increased as well. (the cross coupled caps between the corresponding primary taps on the two OTs perform the same function as the bifilar winding does in the MAC OT, fixing the class B inductive ringing, again, not really a big deal for audio in class AB) The Twin Coupled design is not just a hack job copy of the MAC as some may often think. It's damn close to exact duplication. Of course, the final results will depend on the front end tube circuit design greatly too. And the driver stage has to handle 50% CFB drive levels still. Getting the effective OT primary Z down using high current tubes will reduce the Vac drive requirements for CFB. TV Sweeps for sure.
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Actually, a CCS-loaded pentode with shunt feedback is capable of pretty astounding results as a high-swing driver. I've done experiments that show that I can get a driver with A=10 that can drive my Unity-Coupled output stage to clipping (160Vrms) with .014% distortion, all very low order products. I'm just reluctant to implement it in my amp because the 841s are pretty.
But no joke, the best triode driver I could find to do the job is beat by the pentodes by two orders of magnitude. The pentode drivers have a bunch more bandwidth as well.
This all makes sense... so you're saying that you still keep secret the method and they tried to steal it from you?
How many of the new MC275 were sold? Seems like a lot of people like this stuff...
Am I right that anyone can use the old MC240/275/30/3500 circuits since the patents have run out? I can't see how there wouldn't be a market for a big MC3500 clone. I want one if it sounds as good as our MC240.
What do you I like about the MC240? It just sounds great. We have it paired with JBL L19's and a MC20 preamp and play CD's and vinyl. It just sounds really solid and round, especially with the alnico woofers in the JBL L19s. I'm not going for super high end just mid to hi fi like the MC240 offers. For me trying to go higher you just go crazy. It's like when I drove a Porsche... I was always thinking about something about the car, OCD obsession. I don't want that anymore... (I still own a Porsche, just don't drive it.) I like things done right but opt out of OCD...
So the tube amp guy is an electrical engineer and has his own company, but how many others on here are EE's professionally? I still don't see how the transformers are so difficult if an old lady was doing them by hand in the back room at McIntosh. And I don't even care if it's the same design as a MC240, just so it sounds the same... I'm sure part of the perceived sound is knowing how heavy and solid the amp is physically, none of us can separate perceptions from listening experiences like that, it's part of the hypothalamus.
So for me it doesn't have to be a MC240 but I want that round solid sound I get from it. I also like the cheap Yamaha stereo/radio that I have but the sound is more thin and weak from that device, but not bad... it only costs $45 on ebay. But I'm sure not going to make an event out of listening to it... it was in the garage and then gave it away.
I'm thinking I'd like to try to bi-amp a MC240 but then you get the fact that no two amps sound the same so you'll get different left and right sounds, would be better to do it sideways instead of vertically, but I don't have the L19's cut apart like that...
So what's the cheapest kit I can buy to give me a MC240 sound... the "round" and "strong" and "clean" is what I like compared to a solid state that sounds "thin" and "weak" and "harsh"... I know it's all subjective but I figure you all know what I'm taking about and what I like about the MC240 more than I know...
I'm also happy to see that audio is booming again on forums and YouTube, for me at least, it kind of died a lot since Audio magazine went out of business. There used to be 2-3 hi-fi shops in every town and now there are none in most towns, but I'm seeing a lot of cool stuff over the last week on forums and Youtube.
So what's a good kit for me that's better than the MC240? And I can see if there was a cheapish kit for the MC240 nobody would ever buy any other amps, probably wrong, but I wouldn't. In hi-fi you have to differentiate between the rich guys who buy just because it's expensive and never listen to it and the guys who tinker but can't afford a mc240 for $2,000+.
How many of the new MC275 were sold? Seems like a lot of people like this stuff...
Am I right that anyone can use the old MC240/275/30/3500 circuits since the patents have run out? I can't see how there wouldn't be a market for a big MC3500 clone. I want one if it sounds as good as our MC240.
What do you I like about the MC240? It just sounds great. We have it paired with JBL L19's and a MC20 preamp and play CD's and vinyl. It just sounds really solid and round, especially with the alnico woofers in the JBL L19s. I'm not going for super high end just mid to hi fi like the MC240 offers. For me trying to go higher you just go crazy. It's like when I drove a Porsche... I was always thinking about something about the car, OCD obsession. I don't want that anymore... (I still own a Porsche, just don't drive it.) I like things done right but opt out of OCD...
So the tube amp guy is an electrical engineer and has his own company, but how many others on here are EE's professionally? I still don't see how the transformers are so difficult if an old lady was doing them by hand in the back room at McIntosh. And I don't even care if it's the same design as a MC240, just so it sounds the same... I'm sure part of the perceived sound is knowing how heavy and solid the amp is physically, none of us can separate perceptions from listening experiences like that, it's part of the hypothalamus.
So for me it doesn't have to be a MC240 but I want that round solid sound I get from it. I also like the cheap Yamaha stereo/radio that I have but the sound is more thin and weak from that device, but not bad... it only costs $45 on ebay. But I'm sure not going to make an event out of listening to it... it was in the garage and then gave it away.
I'm thinking I'd like to try to bi-amp a MC240 but then you get the fact that no two amps sound the same so you'll get different left and right sounds, would be better to do it sideways instead of vertically, but I don't have the L19's cut apart like that...
So what's the cheapest kit I can buy to give me a MC240 sound... the "round" and "strong" and "clean" is what I like compared to a solid state that sounds "thin" and "weak" and "harsh"... I know it's all subjective but I figure you all know what I'm taking about and what I like about the MC240 more than I know...
I'm also happy to see that audio is booming again on forums and YouTube, for me at least, it kind of died a lot since Audio magazine went out of business. There used to be 2-3 hi-fi shops in every town and now there are none in most towns, but I'm seeing a lot of cool stuff over the last week on forums and Youtube.
So what's a good kit for me that's better than the MC240? And I can see if there was a cheapish kit for the MC240 nobody would ever buy any other amps, probably wrong, but I wouldn't. In hi-fi you have to differentiate between the rich guys who buy just because it's expensive and never listen to it and the guys who tinker but can't afford a mc240 for $2,000+.
McIntosh O/P transformers
Great thread guys and thanks to Tublab for your excellent posts.
I own a pair of MI350's (The industrial version of the MC3500) and you can view my restoration here and others.
Zed Audio
I have owned every McIntosh MC tube amplifier, Marantz 8B, Marantz 9, HK Citation II, Dynaco ST70 and none come even close to the performance of the MI350s.
Yes I did extensive mods to mine and they sound far better than stock.
There are few today who have the knowledge and/or machinery to re create these O/P trannies especially those from the MI350/MC3500 and also the MI-200. The C cores are not easy to come by and if you want to just have 2 trannies made it may not be possible to purchase the cores for such a quantity.
No everyone does not need a 350w mono block but power aside not one of my other tube amps came close. Had to sell of all as my "better half" insisted that I keep just one pair. Well the MI350s were those I kept.
Steve Mantz Zed Audio Corp.
Great thread guys and thanks to Tublab for your excellent posts.
I own a pair of MI350's (The industrial version of the MC3500) and you can view my restoration here and others.
Zed Audio
I have owned every McIntosh MC tube amplifier, Marantz 8B, Marantz 9, HK Citation II, Dynaco ST70 and none come even close to the performance of the MI350s.
Yes I did extensive mods to mine and they sound far better than stock.
There are few today who have the knowledge and/or machinery to re create these O/P trannies especially those from the MI350/MC3500 and also the MI-200. The C cores are not easy to come by and if you want to just have 2 trannies made it may not be possible to purchase the cores for such a quantity.
No everyone does not need a 350w mono block but power aside not one of my other tube amps came close. Had to sell of all as my "better half" insisted that I keep just one pair. Well the MI350s were those I kept.
Steve Mantz Zed Audio Corp.
Somebody above mentioned the most direct route - get a pair of 240s and restore them. There’s no way you can get the transformers made for less, since they were a very specific design and it’s not just a couple coils of wire around some M6 laminations. If you want an 240 clone.
If you are interested in building a tube amp of some design that has wonderful performance, there are a lot of choices. But it’s not going to be a 240, so you may not be interested.
Some very smart and extremely knowledgeable people have responded to your question, and if they say it’s going to be a challenge, it will be.
That said, it would be a fantastic project and I think you should pursue it. First job? Find somebody who is willing to make the OPTs and commission them.
If you are interested in building a tube amp of some design that has wonderful performance, there are a lot of choices. But it’s not going to be a 240, so you may not be interested.
Some very smart and extremely knowledgeable people have responded to your question, and if they say it’s going to be a challenge, it will be.
That said, it would be a fantastic project and I think you should pursue it. First job? Find somebody who is willing to make the OPTs and commission them.
Hypersil or Hipersil seems to be Westinghouse's trade name for M-6 steel. The real criteria would be what material thickness was used to make the cut cores. Thin material having less loss at high frequency.
Today, a high quality xfmr cut core development would be looking at amorphous steel or nano-crystalline steel. Or, at the very least, Hi-B grain oriented steel, which is an improved version of M-6.
---------------------------------------
Re: SpreadSpectrum
I guess that high performance shunt Fdbk pentode driver you mentioned was a high gm tube. Other than the OT, the driver stage is the other key item for running a 50% CFB design. The 6DJ8/EC88 driver stage used in the MC 3500 design is probably max'd out for headroom. They may have even exceeded the ratings of the tube to get there.
With a couple of Edcor OTs for a Twin Coupled arrangement, and your pentode driver, and maybe a 6F12P front end/splitter, the design may be almost trivially straightforward, other than getting some local and global N Fdbks stable, which might still be arduous. Throw in a Hosfelt PS-500XT power supply from Ebay and we have maybe a 4 or 5 weekend breadboard project - hopefully. Not including any bullet-proof 50 lb chassis.
Today, a high quality xfmr cut core development would be looking at amorphous steel or nano-crystalline steel. Or, at the very least, Hi-B grain oriented steel, which is an improved version of M-6.
---------------------------------------
Re: SpreadSpectrum
I guess that high performance shunt Fdbk pentode driver you mentioned was a high gm tube. Other than the OT, the driver stage is the other key item for running a 50% CFB design. The 6DJ8/EC88 driver stage used in the MC 3500 design is probably max'd out for headroom. They may have even exceeded the ratings of the tube to get there.
With a couple of Edcor OTs for a Twin Coupled arrangement, and your pentode driver, and maybe a 6F12P front end/splitter, the design may be almost trivially straightforward, other than getting some local and global N Fdbks stable, which might still be arduous. Throw in a Hosfelt PS-500XT power supply from Ebay and we have maybe a 4 or 5 weekend breadboard project - hopefully. Not including any bullet-proof 50 lb chassis.
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"Old ladies" RULE electronics. Mac's Sandy West. The gal at Fender (Abigail Ybarra) who wound most of the pickups through the golden era and beyond. The unsung women who strung microscopic beads on hair-wires for core memory. ALL the women who assembled vacuum tubes by hand. Even mundane bits like assembling switches for Japanese radios. And these were not "unskilled" jobs. It took some years for a bright worker to get really consistently good at one job (why we see a few being retained for 40-50 years).
Stereopal.com - McIntosh Factory Tour
YouTube
"Queen of Tone" Abigail Ybarra Talks Fender History and 57 Years of Pickup Winding
YouTube
YouTube
https://youtu.be/UIBceKSvtcM?t=28
The rather-dull book Capital Moves cluelessly follows RCA's hiring of women to assemble radios then TVs. It gives some insight into why women were hired, and served well, and were exploited, and the resulting disturbances.
Stereopal.com - McIntosh Factory Tour
YouTube
"Queen of Tone" Abigail Ybarra Talks Fender History and 57 Years of Pickup Winding
YouTube
YouTube
https://youtu.be/UIBceKSvtcM?t=28
The rather-dull book Capital Moves cluelessly follows RCA's hiring of women to assemble radios then TVs. It gives some insight into why women were hired, and served well, and were exploited, and the resulting disturbances.
There are a lot of EE's here, and other engineers as well. They don't always advertise it. You've already heard from at least 3 EE's in this thread, and you'd be quite surprised to know how many amplifiers one of them has designed/manufactured over the past 4 decades.
Bottom line- there is an immense amount of knowledge and experience here, look around some.
even if there is no Menno's name on particular page , that's it. there is "contact" button , so ...
TOROIDAL TRANSFORERS - Introduction
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Is this the classic "unity coupled" transformer being made in this video? It doesn't look like it's more complex than an ordinary transformer and it's not using silver wire according to the voice-over in the video.
YouTube
What was the difference between the MC275 transformers and the MC240 (original versions.)
Got it... good idea to find some burned out MC240s... How much do those go for?
I appreciate all the help.
I still don't know what it means when someone says they've wound the transformers and someone bought them then tried to unravel them... does that mean that this is like a trade secrete and those that know don't like to share unless they are paid?
Also what's so big about this C core that I keep hearing about? Is it an ancient Myan artifact? Sounds like it.
You see, I get that all you guys are smart, and are way more smarter than me and way more experience about all this stuff too, that's why I'm asking you the questions... but I'm smart too, and have actually had a MC240 my entire life, along with a C20 preamp and other tube stuff and old to me stuff audio stuff. I also have a similar education to an EE and at a one of the world's major universities, so I'm no dummy, I just don't know much about the specifics like you guys do, and I don't work in this field. I do know enough that I know that a transformer is a thing, it's not a God. It's made of wire. And nowdays there are so many more complex things than a tube amp that we carry around in our pockets and I think we all have to let go of the idea of the "mystical secrets" behind the McIntosh transformers. Is it possible to get one of you to teach me how to make one? How much would that cost? The video said that the MC275 has two output transformers... I'm guessing they are wired in a way that they call them the "unity coupled transformer?" Perhaps they are wired out of phase so they cancel out the noise? Is that it?
Also would it be illegal to sell a MCXXX clone due to some copyright or patent?
I also read that the MC30 sounds better than the MC275 and MC240 because the MC30 is all tube and the 275/240 have some other none tube in them, can someone explain that to me? I would just think that the MC30 is the same as the rest but it's lower power so it has less noise so it sounds better, but it's not really better, just less powerful. I'm probably wrong, but want to know.
Is there another kit/design that sounds like a MC240 that's cheaper that I should look at? I like the idea of more power but not if it doesn't sound as good as the MC240, which a lot of people I've read says that the 275 doesn't sound as good as the 240... and that the new 275 doesn't sound as good as the old one... I can see that since it seems the new one is on a circuit board, I can't see that sounding as good as solid wire (much bigger wire too) and air.
Again, I'm not trying to tell anyone that you are wrong and I'm thankful for all of your help, I just have more questions.
I've heard that, but I don't understand why she's the only one and didn't the person up a few posts say they know how to do it and the german person rolled some transformers for a mc3500? ... I get she must have a lot of practice at it... is she still alive? What's her full name?
The new MC275 transformers are made with an automated, computer controlled machine rolling several of them at the same time and they seem to be perfectly spaced... I don't know a lot about transformers but I read that some of the old mc stuff wasn't wound perfectly... and some failed... would silver wire in the MC275 sound better? What about gold or some other rare metal like titanium or platinum wires? (serious questions and not trying to be disrespectful)
Again I don't know much about transformers, but I think some simple tricks could be done to improve the MC ones if you don't try to make them the same size.
And comparing this video with the newer video I posted above... it really looks like the new computer controlled transformer winder creates cleaner wrapping and spacing of the wires then the manual version... but maybe the irregularities of hand winding sound better?
YouTube
Here's how you can reverse engineer a transformer to find the turns and such... not sure it works with the MC240 type transformers?
YouTube
I've actually found a document outlining the exact info (turns, circuit, wire types, etc.) for the unity coupled transformer invented by McIntosh in 1948...
YouTube
What was the difference between the MC275 transformers and the MC240 (original versions.)
Got it... good idea to find some burned out MC240s... How much do those go for?
I appreciate all the help.
I still don't know what it means when someone says they've wound the transformers and someone bought them then tried to unravel them... does that mean that this is like a trade secrete and those that know don't like to share unless they are paid?
Also what's so big about this C core that I keep hearing about? Is it an ancient Myan artifact? Sounds like it.
You see, I get that all you guys are smart, and are way more smarter than me and way more experience about all this stuff too, that's why I'm asking you the questions... but I'm smart too, and have actually had a MC240 my entire life, along with a C20 preamp and other tube stuff and old to me stuff audio stuff. I also have a similar education to an EE and at a one of the world's major universities, so I'm no dummy, I just don't know much about the specifics like you guys do, and I don't work in this field. I do know enough that I know that a transformer is a thing, it's not a God. It's made of wire. And nowdays there are so many more complex things than a tube amp that we carry around in our pockets and I think we all have to let go of the idea of the "mystical secrets" behind the McIntosh transformers. Is it possible to get one of you to teach me how to make one? How much would that cost? The video said that the MC275 has two output transformers... I'm guessing they are wired in a way that they call them the "unity coupled transformer?" Perhaps they are wired out of phase so they cancel out the noise? Is that it?
Also would it be illegal to sell a MCXXX clone due to some copyright or patent?
I also read that the MC30 sounds better than the MC275 and MC240 because the MC30 is all tube and the 275/240 have some other none tube in them, can someone explain that to me? I would just think that the MC30 is the same as the rest but it's lower power so it has less noise so it sounds better, but it's not really better, just less powerful. I'm probably wrong, but want to know.
Is there another kit/design that sounds like a MC240 that's cheaper that I should look at? I like the idea of more power but not if it doesn't sound as good as the MC240, which a lot of people I've read says that the 275 doesn't sound as good as the 240... and that the new 275 doesn't sound as good as the old one... I can see that since it seems the new one is on a circuit board, I can't see that sounding as good as solid wire (much bigger wire too) and air.
Again, I'm not trying to tell anyone that you are wrong and I'm thankful for all of your help, I just have more questions.
I've heard that, but I don't understand why she's the only one and didn't the person up a few posts say they know how to do it and the german person rolled some transformers for a mc3500? ... I get she must have a lot of practice at it... is she still alive? What's her full name?
The new MC275 transformers are made with an automated, computer controlled machine rolling several of them at the same time and they seem to be perfectly spaced... I don't know a lot about transformers but I read that some of the old mc stuff wasn't wound perfectly... and some failed... would silver wire in the MC275 sound better? What about gold or some other rare metal like titanium or platinum wires? (serious questions and not trying to be disrespectful)
Again I don't know much about transformers, but I think some simple tricks could be done to improve the MC ones if you don't try to make them the same size.
And comparing this video with the newer video I posted above... it really looks like the new computer controlled transformer winder creates cleaner wrapping and spacing of the wires then the manual version... but maybe the irregularities of hand winding sound better?
YouTube
Here's how you can reverse engineer a transformer to find the turns and such... not sure it works with the MC240 type transformers?
YouTube
I've actually found a document outlining the exact info (turns, circuit, wire types, etc.) for the unity coupled transformer invented by McIntosh in 1948...
What did I do for a living before retirement? Designed those "more complex things" at Motorola.
During the 41 years I worked there I saw the cell phone evolve from a 20 pound back pack that was worn by a soldier to the little plastic thingy that our world has become dependent on. That knowledge was not gained overnight, nor fully understood by any single person.
Again, the McIntosh amp design evolved over time from the vacuum tube radios of the 1920's. So did most of the other popular amp designs of the tube HiFi era. The McIntosh design just took a slightly different path early on in it's development, The Porsche and the VW Beetle are both cars. Their development paths differed years ago, yet one hybrid existed, the 914.
The Crowhurst twin coupled design previously mentioned is the 914 of the Mac world. It can be made without the "mystical secrets" of the Mac transformers. As with the 914, many enthusiasts shun it as not a real Mac / Porsche. Will it satisfy you?
I don't know. If not, you or someone who can make transformers needs to learn the secrets.
It was an EL34 @ 10mA. I was experimenting with that because I wanted to see if it would work well to drive anything up to a CF output stage. I got up past 320Vrms with very low distortion. I needed a tube that could eat a high idle plate voltage to get up to 300Vrms+ and EL34 was the easiest to get my hands on.
Unity-Coupled output stage driver would be easier than that since driver idle plate voltage could be lower than the power tube, and B+ for the driver could be a tube plate. Normally this would give positive feedback to the driver like in the Mac amps but the CCS would block all but a miniscule amount.
One thing I learned from experiments was that true pentodes have lower distortion than beam tubes in this configuration. I think beam tubes get a bit kinky at low plate voltages and currents. They still have low distortion but true pentodes are quite a bit lower.
One thing I want to try is playing with small supressor grid biases to see if that lowers distortion yet further in that low plate voltage, low plate current zone.
Unveiling the "Mystique"
mc240 has listened to the MC3500 and has been very impressed.
Several significant factors coalesce in the MC3500 that have nothing to do with special OT xfmrs. The amplifier is high power, 350 W, high Neg. Fdbk.
and uses TV Sweep tubes.
High neg. Fdbk makes for very low distortion, but often causes nasty clipping artifacts, UNLESS the amplifier POWER is high enough to handle all signal peaks consistently. The 350 W MAC passes the test easily here.
Bass slam and high speaker damping factor derive from high current capability and high neg. Fdbk. Again the MAC passes the test easily with 8 Sweep tubes. Big TV Sweep tubes have amazing peak current handling capability, and the MAC is using plenty of neg. Fdbk including the high 50% CFB.
A driver stage that can handle the high % CFB grid signals is ESSENTIAL too, and the MAC uses a bootstrapped driver for that. SpreadSpectrum's shunt Fdbk pentode driver stage may well outperform the MAC triode driver stage.
I would surmise that duplicating these factors alone would give one 99% of the MAC 3500 sound.
If you really HAVE to have the Unity Coupling for fixing class B inductive artifacts, then going to the Twin Coupled design with cross coupling caps between the OTs fixes that too. No kookie bifilar OTs needed at all. Although none of this is really an issue for audio amplifiers running class AB (to avoid crossover distortion gm variation artifacts)
I would say that the Twin Coupled design is actually OVER-KILL, but easy enough to build, and it gets you conveniently (with readily available 100 Watt OTs) to the 200 Watt level for the 1st criteria above.
The great mystery MAC OTs have been producing a phantom roadblock for 70 years. A mirage. You can drive right thru it.
You could also use a Circlotron design, like ElectroVoice did, to achieve the same results. They just never made a 350 Watt version with TV Sweep tubes to get in the Hall of Fame.
The real road block to producing MAC 3500 clones is the seriously declining stock of BIG TV Sweep tubes. Some Chinese EL509 tubes around yet I think.
-------------------------------------------
Re: SpreadSpectrum
Interesting that true pentode is working best.
mc240 has listened to the MC3500 and has been very impressed.
Several significant factors coalesce in the MC3500 that have nothing to do with special OT xfmrs. The amplifier is high power, 350 W, high Neg. Fdbk.
and uses TV Sweep tubes.
High neg. Fdbk makes for very low distortion, but often causes nasty clipping artifacts, UNLESS the amplifier POWER is high enough to handle all signal peaks consistently. The 350 W MAC passes the test easily here.
Bass slam and high speaker damping factor derive from high current capability and high neg. Fdbk. Again the MAC passes the test easily with 8 Sweep tubes. Big TV Sweep tubes have amazing peak current handling capability, and the MAC is using plenty of neg. Fdbk including the high 50% CFB.
A driver stage that can handle the high % CFB grid signals is ESSENTIAL too, and the MAC uses a bootstrapped driver for that. SpreadSpectrum's shunt Fdbk pentode driver stage may well outperform the MAC triode driver stage.
I would surmise that duplicating these factors alone would give one 99% of the MAC 3500 sound.
If you really HAVE to have the Unity Coupling for fixing class B inductive artifacts, then going to the Twin Coupled design with cross coupling caps between the OTs fixes that too. No kookie bifilar OTs needed at all. Although none of this is really an issue for audio amplifiers running class AB (to avoid crossover distortion gm variation artifacts)
I would say that the Twin Coupled design is actually OVER-KILL, but easy enough to build, and it gets you conveniently (with readily available 100 Watt OTs) to the 200 Watt level for the 1st criteria above.
The great mystery MAC OTs have been producing a phantom roadblock for 70 years. A mirage. You can drive right thru it.
You could also use a Circlotron design, like ElectroVoice did, to achieve the same results. They just never made a 350 Watt version with TV Sweep tubes to get in the Hall of Fame.
The real road block to producing MAC 3500 clones is the seriously declining stock of BIG TV Sweep tubes. Some Chinese EL509 tubes around yet I think.
-------------------------------------------
Re: SpreadSpectrum
Interesting that true pentode is working best.
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@ mc240: In #32 you're showing quite some profund lack of knowledge to us:
1st: As the MC275 is, alike the MC225 and MC240, stereophonic, i.e. a two channel amplifier, it is quite expectable that it has two output transformers.
2nd: We know that silver is the best electrical conductor, followed by copper, whose electrical conductivity is just about 6 % worse than silver's. So why bother with silver wires at all? Why should they sound better? Not to speak of the other materials you mentioned, which are even worse (Ti is a bad conductor!)
3rd: Do you really believe you'll find a proud owner of a MC275 in working condition who is willing to let you dismantle one of it's OT's in order to gain detailled informations of how it has been made?
4th: Again, MC240 and MC275 are all-tube amplifiers. No SS in the signal paths.
Btw, the MC275 circuitry has been altered several times. The first OT's featured trifilar primaries, while the last ones are bilfilarly wound.
Best regards!
1st: As the MC275 is, alike the MC225 and MC240, stereophonic, i.e. a two channel amplifier, it is quite expectable that it has two output transformers.
2nd: We know that silver is the best electrical conductor, followed by copper, whose electrical conductivity is just about 6 % worse than silver's. So why bother with silver wires at all? Why should they sound better? Not to speak of the other materials you mentioned, which are even worse (Ti is a bad conductor!)
3rd: Do you really believe you'll find a proud owner of a MC275 in working condition who is willing to let you dismantle one of it's OT's in order to gain detailled informations of how it has been made?
4th: Again, MC240 and MC275 are all-tube amplifiers. No SS in the signal paths.
Btw, the MC275 circuitry has been altered several times. The first OT's featured trifilar primaries, while the last ones are bilfilarly wound.
Best regards!
If I were doing a Unity-Coupled amp today, I'd do it as a Twin-Coupled with normal output transformers.
Circlotron is a very similar form of operation and superior in a few respects but I was always discouraged by the number of floating power supplies necessary. However, I've always been intrigued by it and if I were retired, I'd probably have to build one just to check it off my list.
Circlotron is a very similar form of operation and superior in a few respects but I was always discouraged by the number of floating power supplies necessary. However, I've always been intrigued by it and if I were retired, I'd probably have to build one just to check it off my list.
I own a MAC 1500, almost an MC240 -
"The MAC 1500 puts out 30 watts per channel and is also known for having one of the better headphone sections of any receiver. It apparently has special secondary transformer windings specifically for the headphone output as opposed to the usual resistor placed in the speaker output circuit."
It also has the output tube cathode windings, a design I assume is similar to the MC240. One went for ~$600 on ebay recently, most are set between $1K and 2. I bought mine as an investment 10 years ago; probably not the best financial strategy at that. It sits in a cardboard box in a closet. I would have done better buying $1k of INTC...
Modifications of this unit to put it more close to / exceed the '240 in performance are available, if you look for it, I wish I had the URL for that at the tip of my fingers... Someone here will know.
There's also the MA230, which is similar but without the tuner. I sold a chassis (no glass) for $450 maybe 10 years ago. Current ebay price for a complete one? $2.4k
"The MAC 1500 puts out 30 watts per channel and is also known for having one of the better headphone sections of any receiver. It apparently has special secondary transformer windings specifically for the headphone output as opposed to the usual resistor placed in the speaker output circuit."
It also has the output tube cathode windings, a design I assume is similar to the MC240. One went for ~$600 on ebay recently, most are set between $1K and 2. I bought mine as an investment 10 years ago; probably not the best financial strategy at that. It sits in a cardboard box in a closet. I would have done better buying $1k of INTC...
Modifications of this unit to put it more close to / exceed the '240 in performance are available, if you look for it, I wish I had the URL for that at the tip of my fingers... Someone here will know.
There's also the MA230, which is similar but without the tuner. I sold a chassis (no glass) for $450 maybe 10 years ago. Current ebay price for a complete one? $2.4k
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I have several Hoefer PS-500XT power supplies (Ebay), and a couple of 250 VA medical isolation xfmrs (surplus) to plug them into, to make those into floating B+. Will be a breadboard project some day probably, if I can find a 600 to 800 Ohm primary range OT.
The other approach is to use 120/120////120/120 dual bobbin industrial xfmrs directly to get a floating B+. The Stancor TGC175-230 xfmrs I have, have 65 pf from primary bobbin windings to the secondary bobbin. Usually only 230 VAC available on the secondary though, could do a V doubler I guess,
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