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McIntosh "Samra Style"

52.36.153.100
Posted on January 17, 2017 at 01:49:09
mr9iron
Audiophile

Posts: 454
Joined: March 13, 2002



Many of you inmates have seen some of my Citation restoration posts; something a little different this time...I was wondering if I could get my hands on a pair of McIntosh mono blocks and see what kind of a project it would be to restore and upgrade a pair. Those large chassis seem nice and room-y underneath, easy to work on :).. Of course trying to find something one can afford for that name is tough sledding for a man of "modest means" -Luckily, over the summer, when audio is not so hot on the e-bay market, some bidders fell asleep and I picked up these Mc40's for a decent price. They sat around for little under a year while I researched a restoration plan..



I say "research" but I already had a good idea of what I wanted to do..I had seen Samra's posts on his Mc30's and the like, he's done quite a number of "Macs" recently. I asked him about his "devious methods" and parts selections. Mikey, as per usual was more than helpful, and lent his suggestions. His beefed up power supply with poly-films will really bring out the potential of the "Mac" so I studied his set ups and found sources for the parts. I know you can get the kits, and drop in replacements for these, but those parts do not necessarily yield the best results.



Mikey didn't have to hold my hand as much on this project, as it seems I am getting better at trouble shooting and picking better restoration procedures. However, it always feels like I will succeed when I know he's there to answer specific questions, or even just talk theoretically or in general, he lives for this stuff, and it's almost as if he's a regular help line operator.. :)

Here are some of the highlights:

Panasonic Poly-film filters replace the original B+



Nichicon 820 UF doublers like the Citation mods..



Poly-film bias supply filter



Cree Schottky Diodes



Of course, K40 and Vitamin Q coupling caps to replace the old Spragues.



This is how they arrived, of course I did my usual clean up and spit polish.






With a decent quad of Russian KT66 and all this work, I bench tested these amps with a perfect 1khz wave and they easily put out 57 watts RMS. The amps are dead silent at idle, thanks in part to the power supply and a 12 gauge ground bus I installed..



Now I know the MC 40's are not the darling of the McIntosh line up, but when you use the "Samra" formula these guys "shit and git".. and at the same time remain quite musical. Tight control on the bottom end for a tube amp, yet graceful clear and very "layered" from the mid to the highs. I prefer the solid state rectifiers in tube amps. I know many of you will say that's sacrilege, but I like the firmness it provides. It's like you get the best of both worlds. The Schottky Diodes are pretty amazing, this is my first time trying those..



When I first got into tubes I picked up an MC 240, I had it brought up to "working" by a good tech, but I never heard the true potential of the amp, I just thought it was "alright". I ended up selling it due to financial reasons, plus it just didn't quite hit home. Now years later after learning how to do my own restorations, I feel like I finally got to hear what the McIntosh sound is all about, and what these amps can do.. As always a big huge thanks to Mr. Samra.. (Mikey) for showing me the way and making me a "Mac fan"



J

 

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RE: McIntosh "Samra Style", posted on January 17, 2017 at 03:38:38
sony6060
Audiophile

Posts: 1465
Location: USA
Joined: August 8, 2014
 I never heard a coupling capacitor that sounds better than those K40Y-9 that Michael recommends.

As for preamp tubes I would recommend RCA 12AX7 tall grey plate, Brimar 13D5 for 12AU7 and I have no idea for the 12BH7. Michael also likes the RCA tall plate.

 

RE: McIntosh "Samra Style", posted on January 17, 2017 at 03:58:07
rosendds@frontiernet.net
Audiophile

Posts: 599
Location: North East
Joined: November 13, 2010
 Beautiful amps.Mike rebuilt a Mc240 & a MC275 for me with outstanding results.What did you do to make the chrome look so good?

 

RE: McIntosh "Samra Style", posted on January 17, 2017 at 06:25:55
Crazy Dave
Audiophile

Posts: 14371
Location: East Coast
Joined: October 4, 2001
 If I owned those, they'd probably the last amps I would ever own. Beautiful!

Dave

 

Great job!, posted on January 17, 2017 at 07:20:14
FenderLover

One little point... you ever have the line short out, via the metal case of those Russian PIO caps? I usually put Teflon insulation over them, just in case.

Thanks!

 

Like this, posted on January 17, 2017 at 07:24:21
FenderLover
 photo biascircuitchange2_zps4a54826b.jpg

Photo of partial reversion of Fender Bassman circuit.

 

RE: McIntosh "Samra Style", posted on January 17, 2017 at 07:44:49
E-Stat
Audiophile

Posts: 37666
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 Have you tried Mundorf silver foil caps?

 

RE: McIntosh "Samra Style", posted on January 17, 2017 at 08:12:05
sony6060
Audiophile

Posts: 1465
Location: USA
Joined: August 8, 2014
 I have tried the Mundroff silver/oil. A slight harshness in the mids & highs. I went back to K40Y-9.

 

RE: McIntosh "Samra Style", posted on January 17, 2017 at 08:46:33
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi 9Iron, those pictures topped anything I've seen in Absolute Sound, and I thought they were the best I've seen! If you look closely it looks like the previous owner, unless it was you gave those transformers a (Marine boot spitshine) complete with the snapping buffing rag technique.
Those pointers and arrows are great. I never really saw inside a Mac vacuum tube amp. Thanks for the tutorial look....Mark Korda.....P.S. I think Mike S. had to grab the old spittoon to prevent excessive drooling...
.

 

Thanks! -nt, posted on January 17, 2017 at 09:12:52
E-Stat
Audiophile

Posts: 37666
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 .

 

BRAVO, posted on January 17, 2017 at 12:56:35
BillH
Audiophile

Posts: 3913
Location: Baton Rouge
Joined: December 23, 1999
 Well done! Those are beautiful amps, and clean as a whistle.
And 17 wpc above spec. No surprise, of course, but a really nice result.

 

RE: Like this, posted on January 17, 2017 at 13:21:04
mr9iron
Audiophile

Posts: 454
Joined: March 13, 2002
 nice, that's easy enough..good catch, it never crossed my mind until you pointed it out in the images..

thanks!

J

 

RE: McIntosh "Samra Style", posted on January 17, 2017 at 13:34:23
mr9iron
Audiophile

Posts: 454
Joined: March 13, 2002
 hey thanks for the kind words and comments, but I learned most everything from the folks off this forum, Mikey is the best, and most everything I have accomplished in tube restorations is due to his help..

.. and yes I was the culprit that polished out the transformers on these, you can see from the other images they arrived all oxidized and plastered with old tape residue....

if you like this post you might also like my Citation II thread, the images are just as good if not better. I had better light to take the shots on that post..

 

RE: McIntosh "Samra Style", posted on January 17, 2017 at 13:52:54
mr9iron
Audiophile

Posts: 454
Joined: March 13, 2002
 The chrome is very very tedious to do on the mac or any screen plated chrome surface, as any mis- step will remove the silk screen (the only thing harder is oxidized untreated aluminum, in that case you are SOL and look to have it re- lettered after resurfacing)..

It's a multi-step process that starts with a damp sponge, dish soap, and a couple of nights with a q-tip to avoiding the silk screen. Fist run is Noxin 7, followed by collinite 840 cleaner, and then collinte 845, you can go over the silk screen very lightly with the 845 and a soft cotton rag. You don't really hit those screened areas, you just kind of "cheat it."

The transformers you can do the same way, except instead of noxin 7 use McGuires or any 3000+ cutting compound.

J

 

Beautiful Job., posted on January 17, 2017 at 14:53:19
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Jeff
Thanks for the kind words. That 100uf blue cap you used in the FB loop is a Philips BC,right? At first, I thought it was a Xicon but upon closer inspection it looks to be a Philips BC.I always use the Muse KZ there but the BC are excellent caps.
Next,get rid of that God awful selection you were playing.My cat hissed when she heard it and she never does that. haha
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Beautiful Job., posted on January 17, 2017 at 16:33:27
mr9iron
Audiophile

Posts: 454
Joined: March 13, 2002
 yes Mikey you are right, it's def not a Xicon anyway, the color is misleading..I got those from mouser. Yeah I like the Muse too, but I wonder if I got too specific on the search criteria and maybe the Muse didn't show up for those values, but yeah those are great..

I'll see what cat friendly recordings I have next time :)

 

Funny..., posted on January 17, 2017 at 17:23:04
DeKay
 I missed the video link before and just played it.

Didn't know our male cat was resting on the window sill (behind the curtain) until the music kicked in and he bolted off and out of the room.

Not kidding.

 

RE: McIntosh "Samra Style", posted on January 25, 2017 at 12:11:40
rickl
Audiophile

Posts: 583
Location: Twin Cities
Joined: February 7, 2002
 This is one of the bests posts in a long time. Thanks. I'm applying this to another tube restoration.

thanks for the time posting.
looking for some jazz and a little libations - js

 

RE: McIntosh "Samra Style", posted on January 25, 2017 at 13:56:59
mr9iron
Audiophile

Posts: 454
Joined: March 13, 2002
 every so often I get the ambition to post... np and good luck on your restoration..

 

RE: McIntosh "Samra Style", posted on August 27, 2017 at 15:12:09
BillWojo
Audiophile

Posts: 186
Location: NJ
Joined: July 7, 2017
 When I had a friend rebuild my MC40 monoblocks I got rebuild kits from Jim McShane. It included Russian coupler caps like this unit. So far every other amp that I have put in my system doesn't come near this. Recently added a VTA SP9 preamp and my Altecs have never sounded this good.

BillWojo

 

RE: McIntosh "Samra Style", posted on August 27, 2017 at 16:31:31
Lee of Omaha
Dealer

Posts: 1800
Location: Omaha NE
Joined: September 8, 2006
 One further suggestion. Replace the 12AU7 with a 6CG7/6FQ7. The difference is well worth the relatively cheap tube and the 15 minutes rewiring the heater pins.

 

+1 and assuming the 12AU7 is the splitter, I'd add a FET CCS, posted on August 28, 2017 at 20:10:51
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
 and put the 6CG7 in LTP mode.


Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

RE: McIntosh "Samra Style", posted on February 7, 2023 at 18:14:24
mr9iron
Audiophile

Posts: 454
Joined: March 13, 2002
 Hey all, the server I used for uploading images has since long been abolished.

I get lots of requests for the pictures I used to show the work done on my projects. Many want to know the parts and how I installed them and without the pictures it's hard. I was e-mailing them per individual request, and digging up all the files every time. I went through the post and re-uploaded to AA and put them in the order they originally appeared.

This is a good example of how you can restore your Mac tube amps so it's a popular resource it seems.

take care all,

Jeff

 

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