Mcintosh Output Transformers

[fdegrove]

7591A??

Hi,

They're probably made to order for New Sensor.
From the pic at the EH site I would call these 5881 which is a rugged 6L6 anyway.

If I'm not mistaken the original 7591A was especially designed for Fisher,as was the 8417.

The US 7xxx range were mostly special audiotubes:

7025 7027 7591 and so on.

Cherio,😉

 

[SY]

Frank, dshortt9, the issue of Audio was December '91. I've got it in front of me at the moment. On p. 60, Bascom King shows some characteristic curves of a 6JN6 sweep tube being used in a screen-drive configuration at very low currents. The curves look a lot like the most linear triode you've ever seen.

For this particular amp (EA2101), the screens are driven by a 6SN7 cathode follower. Berning did the same thing in the EA230 amp. In his first screen-drive design, the Audionics BA150, he used bipolars in emitter follower configuration to drive the screens. That amp also ran close to class B, getting 150 watts from a single pair of 6LF6s. My amp uses mosfets to drive the screens, Just Because.

Sweep tubes are cool; they're low mu triodes trapped in a pentode envelope.

 

[fdegrove]

SWEEP CLEAN.

Sy,

Thx for the info.
It just makes me wonder what it could do for an OTL designed that way using the ubiquitous EL509/6KG6.

Food for thought,😉

 

[SY]

It should work, but really, there are better tubes for OTL use. That big Russian jobbie (can't remember the number, 6pi-something-or-other?) looked promising. The big, low Rp triodes like the 6336 and 6528 also seem more optimum for that application. Sweep tubes are best for swinging a lot of volts, given their higher Rp and lower gm.

 

[fdegrove]

SWEEPERS CREEPERS

Hi SY,

It may surprise you but the sweeptubes can put out quite a bit of current too.
Once you use them in pseudo triode mode they're pretty linear as well.
I think Alan Kimmel has one going and I've heard some OTLs int he past using this type of tube that sounded awesome.

The big, low Rp triodes like the 6336 and 6528 also seem more optimum for that application. Sweep tubes are best for swinging a lot of volts, given their higher Rp and lower gm.

I use the 6080,it is very good sounding and is one of the cheapest power triodes around.NOS they should cost no more then 10 bucks a pop.

The Russian one currently still in production are the smaller 6C19P
and the huge (but not very reliable) 6C33-C.
They also still manufacture the 6AS7G that Atmasphere is using.

6336A,here you will often find pull-outs and to me they're not as reliable as the 6AS7G family and their interelectrode capacitance gives too much roll off when paralelled.

6528 has a bit higher mu than a 6080 and if it was just as available and cheap I might consider it as well.

Once there was a fabulous tube made by Sylvania,mucho power and a very low Rp.
Unfortunately I never found a source carrying it though.

Cheers,😉

 

[SY]

Yes, sweep tubes can swing some current- mine are loaded with 1250 ohms plate-to-plate. But they have higher perveance than the big-boy triodes, and their current capacity, though high, is still less. Nonetheless, there have been commercial OTLs with sweep tubes, probably because of (at the time) high cost and low availability of the big triodes. And also, running pentode in an OTL is more efficient, an important consideration for commercial product.

The 6528 also has at least double the plate dissipation of a 6080.

 

[DrDeville]

Here is the thread in question...

The cathode winding was used for feedback in the classic Mac circuits. The advantage was lowered distortion. The disadvantage was high drive voltage requirements, which Mac accomplished by a bootstrap of the driver stage (positive feedback).

Norman Crowhurst had an excellent analysis and comparison in his book and in several of his articles in "Audio Engineering."

Hi Sy,

Can you provide a source for these articles? I've looked around, but been unable to find them.

Best,

George Ferguson

 

[fdegrove]

Hi,

Not SY but:

NORMAN CROWHURST.

To download asap.😉

 

[SY]

Great find, Frank.

Also, see "Realistic Audio Engineering Philosophy", Audio Nov 1959, p 52. It may be reprinted in the Audio Anthology series, probably volume 5 or 6.

 

[DrDeville]

Great find, Frank.

Agreed. Crowhurst's articles are a must-read for any newbie. Very clear and useful. Unfortunately, the AudioXpress reprints stop just before the acticle that promises to discuss "special kinds of output arrangments.

Anyone have a source for those articles?

Also, see "Realistic Audio Engineering Philosophy", Audio Nov 1959, p 52. It may be reprinted in the Audio Anthology series

Yep, volume 5.

Can you point me to a source of old Audio magazines? I haven't found one yet. Can't seem to find them at local libraries.

Also, which Crowhurst book do you mean, SY? I enjoy Crowhurst enough that I would buy his book, if he has one on tube audio.

Best,

George Ferguson

 

[SY]

"Understanding Hi Fi Circuits". Priceless.

 

[fdegrove]

Hi George,

Most of the stuff SY and myself relate through when talking tubes was published from the late Seventies onwards, the magazines that is....

When we talk wine, it becomes a totally different decade...😉

Anyway, AudioXpress should have some CDs with older issues you may want to buy.
Mags such as The Audio Amateur, Speaker Builder (if you're into that), Glass Audio .

The Audio Anthology reissues are worthwhile, I only have #1 through #4...too much sand stuff later on...

If you visit E-bay on a regular basis look for the Radiotron Designers Handbook, a must have.

Antique Electronic Supply in Tempe AZ, has some interesting books. As does George H. Fathauer, the previous owner, in short there's enough to keep you busy for ages.

On the more technical side there's John Broskies' chef d'oeuvre online at tubecad.com.

If you read French then almost all issues of "L'Audiophile" can be bought on CD as well, these are still groundbreaking articles filled with innovative, yet well founded thinking.

Than there's Eisenson's cute but shortlived TU-BE OR NOT TU-BE with a lot of pioneering work and lateral thinking. A copy may be hard to find though.

Not always tube or audio related but worth having nonetheless are most 1955-197x? issues of Electronics World and similar publications.

I'm sure I must have forgotten at least a dozen, this was just a "from the top off my head" kind of reply....

Cheers,😉

 

[DrDeville]

"Understanding Hi Fi Circuits". Priceless.

Oooh... sounds good!

Searching on Amazon... no joy.

Searching on Google... BINGO!!

AudioExpress has it! :

http://www.audioxpress.com/bksprods/books/bkaa63.htm

And Chapter 2 is "Special Output Stages"

224 pages, for $15. This has to be the deal of the century.

I'm as happy as a little girl! 😉

Thanks SY. If you hadn't given me the specific title, I never would have found it--I've searched and bought on AudoXpress before, but never found this one--it was under General Audio Reference, and I never thought to look there.

And thanks Frank, for all the great references:

If you visit E-bay on a regular basis look for the Radiotron Designers Handbook, a must have.

Actually, AudioXpress had it on CD-ROM, all cross-referenced. I have it, and I believe it is 1500+ pages 'o joy!

Man, there is so much fun stuff to learn. It's like drinking out of a fire hose.

Thanks Fanatics!

Best,

George Ferguson

 

[Ricdelros]

McIntosh Output transformer

I'm in the process of building mc275 opt. Is there anyone here who knows exactly the impedance of the output transformer's separate feedback winding?. I believe it's a common practice to have 16 Ohms, but I'd like to confirm.

 

[bear]

Re: High quality output transformers

Haven't been reading regularly, and just came across this thread...

I have just found this thread on McIntosh output transformers and thought that I would put in my advice and thoughts.

It would be much to expensive to have a small number of high quality transformers wound with special windings. A much better coice would be to use some of the new and truly outstanding Plitron transformers. These are of special design and many have cathode feedback windings. They are reported to have much better specifications than the McIntosh ones.

I find that Plitron's specs are suspect - unless they changed something radically since the last time I read their specs down into the fine print. There they show tests are very scary low power levels and with nil DC offset. Sorry, I don't want an output transformer that I don't know the full power or -3dB power response, or that will come ungloo'd if there is even minimal DC offset on the primary.

Personally, of the "standard" outputs I'd use Lundahl or Sowter before I'd consider Plitron's offerings... but that's only my opinion.

If I were to build a MC275 or similar circuit these would be my choice. The price is lower than having a limited number of custum ones built. All the engineering has already been done.

A link to the Plitron audio output transformers is:

http://www.plitron.com/Pages/Products/Audio/audio.htm

There are other ways to provide cathode feedback in the output stages, but if you want to keep things simple then the Plitrons are the best way to go.

There is more benefit than just "cathode" feedback at work with a McIntosh output tranny... much wider than usual power bandwidth and really excellent results are the bottom line.

There's nothing that is very complex about the McIntosh circuit...

Not sure I see a bifilar wound with suitable specs and proper windings?? Is there one?

Best regards to all,

John Fassotte
Alaskan Audio

I think that working with the McInstosh output tranny design has significant merit for PP diy'er's tube amps...

_-_-bear

 

[Mark A. Gulbrandsen]

I definately side with John Fosette on this one. The Plitron toroid output trannies are a tough act to beat! Meno Vanderveen(spelling?) did a great job on them. Want to hear how good a toroid output can sound just go listen to any of the BAT power amps that use them. I was the lucky owner of a VK-60 for quite some time and having owned a rather large number of Mac amps over the years, MC-30, MC240, MC275, etc., I can attest that the BAT literally smokes the Mac tube stuff to no end.... its the combination of the 6C33 triodes and the toroid outputs that do it. Sorry but I wouldn't waste my time with ANY Mac stuff again excepting perhaps an MR-78.

Mark

 

[Ricdelros]

McIntosh Output transformer

thanks tony
I had enough information now of mc275 opt.Btw, I's too late that I

have just seen the circuit of mc275 re-issue and commemorative

model because i have already assembled the old type pcb. These

reissue and ce has new approach in circuit and layout, and i doubt

if I'll continue the project because the latter has simple

transformer (no trifilar winding) I want to make it this simple ...

and now here comes mc275G and mc275MkIV. Anyone here who can tell

the differences? Someone told the old one as "the big Bang".

 

[Bandersnatch]

I see there is very little interest.

Depending on amp, the McIntosh used up to 5 side-by-side( Quin-filar?) windings. From the MC30's bifilar moving up to the Tri-filar MC75's...

Shouldn't be too big a deal to take one down, and copy the coil. The interesting part would be figuring out where they simplified for cost reasons and make the improvement. I'd also suggest a different core. High performance material in twin cut C's.

The folks at Heyboer have taken down a few audio outputs, and there are more in the que. No reason not to try a MC output.

Just keep in mind that the McIntosh circuit is based on distributing the load equally between the cathode and plate, and with the pentode amps, conecting the plates to the opposite g2, for full pentode performance.
cheers,
Douglas

 

[bear]

I definately side with John Fosette on this one. The Plitron toroid output trannies are a tough act to beat! Meno Vanderveen(spelling?) did a great job on them. Want to hear how good a toroid output can sound just go listen to any of the BAT power amps that use them. I was the lucky owner of a VK-60 for quite some time and having owned a rather large number of Mac amps over the years, MC-30, MC240, MC275, etc., I can attest that the BAT literally smokes the Mac tube stuff to no end.... its the combination of the 6C33 triodes and the toroid outputs that do it. Sorry but I wouldn't waste my time with ANY Mac stuff again excepting perhaps an MR-78.

Mark

The comparison is not valid. The 6C33 is a VERY LOW plate impedance tube therefore the turns ratio in the output transformer is MUCH closer to 1:1.

ANY transformer used in this way will automatically have apparently better "specs" - and actually will - than an equivalent transformer used for a typical high impedance plate/tube.

Try comparing the Mac output tranny design with another for the same output tube (or impedance) and get back to us on what you find! This is not aimed just at Mark, but everyone... I don't think you all quite understand what it is that the Mac tranny design does, and why.

I'll bet that a Mac style design for the 6C33C will melt the performance of the toroidal Plitron, unless the Plitron is more than a standard Plate ---> secondary design.

Iirc all of the Mac vintage iron was wound on C cores... But there is nothing keeping anyone from employing improved core material, and I do favor C cores myself... getting someone to wind trifilar is another matter - but I know of at least one person who has done this by hand with little problem (probably on a simple winding jig...)

And did you ever try a modified Mac - modern resistors and caps? Improved PS, decoupling, reg fils etc.??


_-_-bear

 

[Reddy KW]

The comparison is not valid. The 6C33 is a VERY LOW plate impedance tube therefore the turns ratio in the output transformer is MUCH closer to 1:1.

ANY transformer used in this way will automatically have apparently better "specs" - and actually will - than an equivalent transformer used for a typical high impedance plate/tube.

Try comparing the Mac output tranny design with another for the same output tube (or impedance) and get back to us on what you find! This is not aimed just at Mark, but everyone... I don't think you all quite understand what it is that the Mac tranny design does, and why.

I'll bet that a Mac style design for the 6C33C will melt the performance of the toroidal Plitron, unless the Plitron is more than a standard Plate ---> secondary design.

Iirc all of the Mac vintage iron was wound on C cores... But there is nothing keeping anyone from employing improved core material, and I do favor C cores myself... getting someone to wind trifilar is another matter - but I know of at least one person who has done this by hand with little problem (probably on a simple winding jig...)

And did you ever try a modified Mac - modern resistors and caps? Improved PS, decoupling, reg fils etc.??


_-_-bear

On board with you. A lot of audio criticism of McIntosh amps is due to the 'don't change anything - it's collectible - we want the original Binghamton dust in the chassis, etc' attitude. And that means tired filter caps, Black Beauty caps turning into resistors, resistors gone way off spec, and so forth.

I've done circuit restorations on a few, including my own pair of 60s, and the difference is not subtle. The usual drill is, the customer shows up with a 275 or something, saying, "I always heard these were good amps but this one sounds dark and heavy and sort of not clear."

So, I change the filter caps (not easy to find), bypass them, put in a fresh set of pp and foil coupling caps (715P is fine) and change out resistors that have wandered away, test/replace tubes, and that's about it.

And every time, the customer calls back with some variation of, "Holy smoke! This thing sounds like a million bucks! Airy! Transparent! And the bottom octave is making the furniture move! You are a genius! (Don't tell them different.)

One fellow even showed back up and gave me $50. Said I didn't charge him enough! The hifi nuts are way different than the guitar amp customers, I can tell you that.

I put a trimpot in the bias circuit of my Mc60s and bias them on the distortion analyzer. They sound very good.