I've never had the chance to listen to any vintage McIntosh stuff but everyone/everywhere seems to rave about them. I have heard some of their newer stuff and really loved it, but its just WAY out of my price range.
So what makes their old tube stuff so sought after? Other than the fact that I think their stuff is cool looking, is there something special/unique about their designs? Are their any clones/schematics available for the DIYer to recreate "the magic?"
Love to hear your thoughts.
So what makes their old tube stuff so sought after? Other than the fact that I think their stuff is cool looking, is there something special/unique about their designs? Are their any clones/schematics available for the DIYer to recreate "the magic?"
Love to hear your thoughts.
I'm with Stuart. It's a very idiosyncratic, very elaborate circuit, with a ton of feedback in two or three nested and partially nested loops. That's what it sounds like; a pentode amp with a lot of gain stages and feedback. 'Transistory' was the first impression I had.
Beautifully built, well engineered (except from an elegance standpoint) and have the very great advantage for a tube circuit of being self biasing, self adjusting, and pretty much immune to variances in the tubes. You can change from the finest Mullard EL34s to unmatched Soviet wafer-based 5881s, and the amp sounds the same.
That's my experience with two examples of the MC240 (EL34 stereo) that I repaired. They're good amps, but undeserving of their iconic status, IMNSHO.
Aloha,
Poinz
AudioTropic
Beautifully built, well engineered (except from an elegance standpoint) and have the very great advantage for a tube circuit of being self biasing, self adjusting, and pretty much immune to variances in the tubes. You can change from the finest Mullard EL34s to unmatched Soviet wafer-based 5881s, and the amp sounds the same.
That's my experience with two examples of the MC240 (EL34 stereo) that I repaired. They're good amps, but undeserving of their iconic status, IMNSHO.
Aloha,
Poinz
AudioTropic
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mcintosh chrome
Best chrome plate in the industry. The tube amps had 3 lb (est.) output transformers, 3 times the size of a Dynaco ST70. In a world where bass sells iron, before transistors, McIntosh was the best I ever heard. In a world after transistors, I doubt if a tube Mac ever blew up a $500 speaker. It would take a vast lightening bolt to get through all that iron. I've always spent 3-5 times the amp cost on my speakers, and I'm a bit sensitive about blowing the speaker. I'm sitting here today, watching my transistor ST120 throw welding sparks from the ring the R27 resistor is soldered to, to the 6-32 nut clamping it down to the output transistor collector. (Infinity ohms). And most of the other transistor amps connect this point directly to the speaker?
Best chrome plate in the industry. The tube amps had 3 lb (est.) output transformers, 3 times the size of a Dynaco ST70. In a world where bass sells iron, before transistors, McIntosh was the best I ever heard. In a world after transistors, I doubt if a tube Mac ever blew up a $500 speaker. It would take a vast lightening bolt to get through all that iron. I've always spent 3-5 times the amp cost on my speakers, and I'm a bit sensitive about blowing the speaker. I'm sitting here today, watching my transistor ST120 throw welding sparks from the ring the R27 resistor is soldered to, to the 6-32 nut clamping it down to the output transistor collector. (Infinity ohms). And most of the other transistor amps connect this point directly to the speaker?
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fuse protection
Fuses have a voltage stop rating. 1/4x1-1/4" fuses are rated either 32 vdc, or 250 VAC. Above that rating the plasma of the fuse lets the arc continue across. Fuses will not stop a lightning bolt. A shorted heavy power transformer might. We get a lot of lightning here in the middle, a strike took out the bus on my Windows 98 computer from the phone line. One hit my ST120, something exploded the neon tube, but no other damage. I know about the MOS device you can install in your electrical box. If you don't check it every day, you don't know it is ruined and unable to stop the next one.
Factories here in the middle use a 10 lb. SOLA transformer on expensive computer controlled production equipment. Keeps the weighers running.
Fuses have a voltage stop rating. 1/4x1-1/4" fuses are rated either 32 vdc, or 250 VAC. Above that rating the plasma of the fuse lets the arc continue across. Fuses will not stop a lightning bolt. A shorted heavy power transformer might. We get a lot of lightning here in the middle, a strike took out the bus on my Windows 98 computer from the phone line. One hit my ST120, something exploded the neon tube, but no other damage. I know about the MOS device you can install in your electrical box. If you don't check it every day, you don't know it is ruined and unable to stop the next one.
Factories here in the middle use a 10 lb. SOLA transformer on expensive computer controlled production equipment. Keeps the weighers running.
Picture is worth......... 
Check out this wonder site for schematics etc
Berner's McIntosh Site
Charles
Check out this wonder site for schematics etc
Berner's McIntosh Site
Charles
Attachments
Thanks for everyone's thoughts on this! So it seems the general feeling is that the design/circuit is nothing to change the world, but McIntosh used good quality parts, made it look great, and built it like a tank. Am I correct? It seems that turned out to be a recipe for success as far as they're concerned.
With all due respect to everyone who answered... I think maybe you have missed some things...
The thing that made McIntosh's reputation is twofold:
1. they were the only manufacturer to successfully employ a cathode winding in the output transformer on a commercial basis.
2. they also made some very high power tube amps using the same output stage technology and a bootstrapped driver. I think one of them was the K-104. I think it used 8005 output tubes...
So, what was it that made any of this special?
Read the chapter in the Radiotron designer's handbook on the McIntosh "design". Many other designs were suggested that used cathode coupled output stages, but none were so elegant as this one.
What it did in one shot was to reduce the primary impedance so that the usual problems in output transformer design that forced a rather limited bandwidth went away. They could get ~100kHz. The other thing that worked nicely is that in class B the crossover notch distortion (iirc) was minimized by the "carry through" of the iron.
The original McIntosh amps did not have multiple nested feedback loops, as far as I can recall.
The big problem with the McIntosh design is that the output stage had "unity gain". That meant that the driver has to swing whatever the output voltage swing (on the primary) happened to be! That is extra swing compared to an output stage that has gain. Sounds familiar to solid state amp aficionados?
This was a major problem in the big amps like the K-104 (it was also made under another model number but it escapes me at the moment) because there was almost 2kV on the plates! The solution was a neat "bootstrap" of the driver tube where it is lifted by the output. Of course keeping that arrangement stable is a bit tricky, but they did it. A worthy schematic to find.
I've seen examples of this amp running, and the 8005s run with the plates cherry red - kewl because these are nude nickel plates!
Unlike many competing amps of the day, the McIntosh's square wave response does not have the typical ringing due to the feedback trying to keep the sagging HF response up (the iron is rolling off), the square wave was nice and clean, usually without any overshoot at all. Clean.
I have a 50-W on my bench - it has an interstage as well, and it is very clean. The Mc30 that used to inhabit that spot was the same.
So, the McIntosh design is/was special, imho.
_-_-bear
The thing that made McIntosh's reputation is twofold:
1. they were the only manufacturer to successfully employ a cathode winding in the output transformer on a commercial basis.
2. they also made some very high power tube amps using the same output stage technology and a bootstrapped driver. I think one of them was the K-104. I think it used 8005 output tubes...
So, what was it that made any of this special?
Read the chapter in the Radiotron designer's handbook on the McIntosh "design". Many other designs were suggested that used cathode coupled output stages, but none were so elegant as this one.
What it did in one shot was to reduce the primary impedance so that the usual problems in output transformer design that forced a rather limited bandwidth went away. They could get ~100kHz. The other thing that worked nicely is that in class B the crossover notch distortion (iirc) was minimized by the "carry through" of the iron.
The original McIntosh amps did not have multiple nested feedback loops, as far as I can recall.
The big problem with the McIntosh design is that the output stage had "unity gain". That meant that the driver has to swing whatever the output voltage swing (on the primary) happened to be! That is extra swing compared to an output stage that has gain. Sounds familiar to solid state amp aficionados?
This was a major problem in the big amps like the K-104 (it was also made under another model number but it escapes me at the moment) because there was almost 2kV on the plates! The solution was a neat "bootstrap" of the driver tube where it is lifted by the output. Of course keeping that arrangement stable is a bit tricky, but they did it. A worthy schematic to find.
I've seen examples of this amp running, and the 8005s run with the plates cherry red - kewl because these are nude nickel plates!
Unlike many competing amps of the day, the McIntosh's square wave response does not have the typical ringing due to the feedback trying to keep the sagging HF response up (the iron is rolling off), the square wave was nice and clean, usually without any overshoot at all. Clean.
I have a 50-W on my bench - it has an interstage as well, and it is very clean. The Mc30 that used to inhabit that spot was the same.
So, the McIntosh design is/was special, imho.
_-_-bear
Always wondering did Mcintosh just reply in his own way(Unity Coupling) to Electro Voice line of cathode coupled(Circlotron)Power Amp(A15 to A100 series).I prefer Electrovoice cyrcuitry(much sympler and efective).Did somebody know chronology or conection betwen this two greath Manufacture and Invention? Know fact that Serbian guy Mioljub(Mile)Nestorovich was the one of the main desingner of Mcintosh Amps in that long passed time.This guy before imigration in the USA worked in Belgrade Institute for Experimental Phonetic,Pahtology of Speak and Reserch of Foreign Languages like Higly Ranked Employ.Here is one file(4Mb, pdf, schematic&text) of Mille Nestorovich from 1961 of 20W laboratory Amp(EFE1),who he developed.I only cant say that guy(Mille)know the job in ewery detail.Pdf file is posible to find in site www.DIYaudio.RS,forum tubes,under name EFE-1 amplifier by Mioljub Mile Nestorovic posted by Zenn Mod.Best Wishes DIY Friends.
The original Mcintosh design was developed by Frank Mcintosh during WW2, in order to keep reasonable distortion in a class B output stage, for an amp made for ships. Its main claim to fame was the reduction of an inductive spike at the crossover between the two output tubes. This was written up in a technical paper in the late 1940's.
Mile was an excellent design engineer who developed another generation of power amp called the Mc 350 or 3500 series. We used them for years with the Grateful Dead sound system. A virtually perfect power amp for most applications.
Mile was an excellent design engineer who developed another generation of power amp called the Mc 350 or 3500 series. We used them for years with the Grateful Dead sound system. A virtually perfect power amp for most applications.
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