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Why Recap Vintage McIntosh Gear


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I purchased a McIntosh C20 preamp on Epay. I was looking for a tube preamp to run with my new to me Khorns. My first Mcintosh piece of gear and I knew the C20 would need some work.

People say...oh keep it original and keep the "bumble bee caps", well that ain't necessarily a good idea. Some might look at the "before specs" and say that the measured performance wasn't 

that bad,but the McIntosh factory baseline for THD is 0.2 or better. I see tons of vintage Mac gear but the sellers never post figures,so I thought I would post these.

When I receive the C20 back from the McIntosh authorized factory dealer service center I'll post my thoughts on the sound with the Khorns.

The tech said "it sounds wonderful and "warm as it should". I can't wait.

 

2021-08-01_08-16-32.png

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1 hour ago, Bubo said:

You replaced the bumble bee caps, with what ?

any difference in measurement ?

Lol...I chuckled,,,sorry. The bumble bee caps are VG candidates to leak and crack. I'm sure though if a put them on ebay somebody will buy them.

The Arizona Capacitors Blue and Red have that classic sound. I tried to voice the preamp with mostly copper foil. I've had the 4 teflons for years and was glad to use

them. The same with the Japanese resistors and the Black Gates. This unit gobbled up a bunch of stuff I've had for quite a while....

 

https://jeffsplace.positive-feedback.com/the-vintage-mcintosh-mx110-adventure-omg-stop-the-presses-up-next-the-a5-vott-project/

 

 I used mostly pieces that I had left over from my other builds.

Mundorf,Miflex KPFM,TFT teflon JDM Duelund,Arizona Capacitor,and Mundorf 4700uf 40v

I purchased the JDM's, the Arizona caps,and the Mundorf filament cap.The rest I had leftover

Takiman and shinko 1 watt resistors both carbon and metal film

Silver micas

4-47uf 16v black gate FK

The tech upgraded the power supply... low esr 105c caps...C1 50/50/50/50 uf electrolytic B+ cap 1 C2 50/50/50/50 uf electrolytic B+ cap

IIRC the original can cap values were like 40,40.40,20,20,20

The original filament cap was a 2000uf 15v replaced w the 4700uf 40v

You can upgrade these C20's with improved performance and yes my build is over the top,You can spend 5 bucks each on caps and no doubt retain the original sound. I just like to experiment. So if I have 4k invested I'd rather do that then spend 10K to each their own.

Will all this make a SQ difference? In my experience yes.

 

I had 4 .022uf Jupiter caps that I was hoping to use but the schematic I grabbed off the web showed them,but they weren't used in the model. McIntosh built 3

versions of the C20...early,mid,and late. Mine is a mid unit with a unpotted transformer and glass faceplate.

 

 

2021-08-01_09-06-27.png

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1 hour ago, billybob said:

Guessing you ran the unit before having the service work and will be able to hear the difference.

No....from the Ebay seller direct to the largest and most respected Mac dealer in the world. The preamp is 60 years old...I voice all my vintage RTR's,Accuphase,and the rest. It's just how I roll.

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If they had better components 50 years ago

they would have used them

 

So why not replace with 1%

and better temp and performance ratings.

Carbon resistors probably don't find their way into many new designs

Same goes for rectifier tubes etc

 

Mac transformers tend to be well engineered.

I believe 2 of the 4 founders were transformer engineers

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1 hour ago, Bubo said:

If they had better components 50 years ago

they would have used them

 

So why not replace with 1%

and better temp and performance ratings.

Carbon resistors probably don't find their way into many new designs

Same goes for rectifier tubes etc

 

Mac transformers tend to be well engineered.

I believe 2 of the 4 founders were transformer engineers

Everything I specified and provided was 1 pct and I used all caps that give a mix of detail,warmth,transparency and no harshness or edge to the music. The preamp should despite the tube rectifier should sound better than new.

 

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28 minutes ago, Fast996 said:

Everything I specified and provided was 1 pct and I used all caps that give a mix of detail,warmth,transparency and no harshness or edge to the music. The preamp should despite the tube rectifier should sound better than new.

 

Can you stuff 2 diodes in the socket for the tube rectifier ?

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40 minutes ago, Bubo said:

Can you stuff 2 diodes in the socket for the tube rectifier ?

In my instructions for the rebuild I mentioned that,but it was never addressed by the tech

 I'm alright with the 6x4 as the C20 doesn't sound like the C22 .

I didn't want to make a change away from original.anyway

At some point ill.probably pick up a C22 and then ill.see which one I prefer.

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18 hours ago, Fast996 said:

Restoration

So it isn’t clear from the page you posted. Did they replace all the caps? The page just talks about cleaning and retensioning the tube sockets. The performance clearly improved, I can’t tell if the caps were changed. 

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56 minutes ago, Pondoro said:

So it isn’t clear from the page you posted. Did they replace all the caps? The page just talks about cleaning and retensioning the tube sockets. The performance clearly improved, I can’t tell if the caps were changed. 

Hi ,

Here is the list of changed parts,all of the capacitors,all the electrolytics,including the power supply which was upgraded to about double the uf. All original spec'd low noise resistors and others upgraded to 1 pct 1 watt and all caps were 1 pct also. Some in spec carbon resistors were left in place.

The best published specs after a recap I could find on the web was a unit done by Terry Dewick a master McIntosh tech. The unit Terry recapped which he called "virgin" was 0.02 THD

Am I happy with .05/.06 absolutely  because mine was electronically far from virgin. Also the new caps should have a very positive effect on the sound...though still having the "Mac" signature. I'm glad I had it done. It will last me the rest of my lifetime.

2021-07-29_14-38-32.png

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3 hours ago, Fast996 said:

Hi ,

Here is the list of changed parts,all of the capacitors,all the electrolytics,including the power supply which was upgraded to about double the uf. All original spec'd low noise resistors and others upgraded to 1 pct 1 watt and all caps were 1 pct also. Some in spec carbon resistors were left in place.

The best published specs after a recap I could find on the web was a unit done by Terry Dewick a master McIntosh tech. The unit Terry recapped which he called "virgin" was 0.02 THD

Am I happy with .05/.06 absolutely  because mine was electronically far from virgin. Also the new caps should have a very positive effect on the sound...though still having the "Mac" signature. I'm glad I had it done. It will last me the rest of my lifetime.

2021-07-29_14-38-32.png

So this is very interesting. Lots of people say, “replace the capacitors” but here is actual before and after test results. Thanks!

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I've walked the walk with vintage Mac for actual operational purpose, where best sonics are a consideration, and I can tell you without question that these pieces benefit from the rework. Collectors who have these sitting on a shelf might well do just fine leaving them original, because after all they are doing it for the collecting, but for actual operational use - not to mention safety - an electronic restoration by a competent technician well versed in reworking these pieces is highly recommended. In this case, we have one who can do their own work and have gotten the requisite excellent results.

 

There's certainly room for discussion as to exactly what parts should be used to best keep the "signature", but I've found that there's more leeway than you might think, just listening to the different builds that I have, but certainly know that a good build does wonders for the pieces. 

 

C22 has a solid state rectifier where the C20 is tube rectified, and that seems to account for the obvious difference in its signature......more authority in the bass response the C20 a bit more "rounded". Both really have a magic about them, though......

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4 hours ago, Audible Nectar said:

 

 

C22 has a solid state rectifier where the C20 is tube rectified, and that seems to account for the obvious difference in its signature......more authority in the bass response the C20 a bit more "rounded". Both really have a magic about them, though......

My C20 will be paired with a PS modded and upgraded Accuphase P300 which is a great SS amplifier....when I upgrade them. I will be interested if a synergy will exist and if the tube rectified C20 will deliver some punch in the bass. One can hope....overall the pairing should deliver some magic. I have tube amps but I'm going to try the Accuphase first.

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Low and behold I didn't notice that the tech did read all of my instructions and replaced the 6x4 tube rectifier with a solid state rectifier.

What difference can I expect to hear. There was a reason he upgraded the power supply.

20210805_071942.jpg

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The solid state rectifier will tighten up the low end. 

 

As as far as recapping goes.....I have recapped five vintage McIntosh components. An MC2105, C32, C34v, and two MC50 ‘s, and all of them came alive afterwards.  Huge difference in sound.  Much cleaner, quieter, and more detailed.

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