McIntosh Re-cap Questions

[Trout]

So,

I have had this McIntosh MC240 sitting on my bench for about a month and a half while I tried to locate the correct old style can caps.

So far the only place that "Has" them advertised Is Zack Engeneering. And they are closed, and have been closed over a month now. Or at least that is what the website says.

So, looking at options, at least options that will not require much butchery, I was wondering if there is any reason I should not try this, Basically, Replacing the pair 100/30 can caps with a 100/100 & a 32/32.

And Replacing the 250uf 250V with a 220uf/385V.

Here is the PS schematic.
Mc240 PS

The chassis shots are on My Restore Page

I can get the complete set of JJ caps for less than the price of 1 100/30 Can cap from Zack's.


As long as I isolate the mounting I see no other reason it should not work?

I have plenty of those phenolic mounting plates as well as a bunch of garolite plate material for mounting.

Yes? No?

Trout

Trout

 

[HollowState]

Hi Trout,

Electrically this is a perfectly acceptable replacement. The fact that the two 100ufd caps are in the same can is of no detriment, and is perhaps better since they are in parallel anyway. The only issue might be the physical size of the dual 100ufd can. But as long as it will fit and can be mounted, your in business. Check the size before you buy.

Happy T day

Victor

 

[Trout]

Hi Trout,

Electrically this is a perfectly acceptable replacement. The fact that the two 100ufd caps are in the same can is of no detriment, and is perhaps better since they are in parallel anyway. The only issue might be the physical size of the dual 100ufd can. But as long as it will fit and can be mounted, your in business. Check the size before you buy.

Happy T day

Victor

Thanks for the response Victor,

I checked the size of the JJ 100/100 500V its actually shorter than the original. 1-3/8" dia. x 2 5/8" height.
The 32/32-500V is 1-3/8" dia. x 2" height

The 220uf/385V is actually smaller than the originals also.
1-3/16 dia. x 2"

So I actually end up pretty close and having extra space to work with.

I guess there is more hope than I thought!!

Shouldnt be to big of a deal to mount them, The access to both sides is actually pretty good. I might as well replace all the electrolytics, There only a handful.

Trout

 

[cerrem]

Call up antique Electronic supply or go to website...They make thier own high quality multicaps that will fit right into the Mac with no mods...

Chris

 

[Burnedfingers]

There is a company in Waterloo, Iowa called Farnesworth electronics that may very well have NOS capacitors that will be 100% of what you need. They were a big time operator years ago and still have 100's of tubes and capacitors left on their shelves.

 

[Trout]

I have checked AES, Those Mallory's they sell are not the correct value, They do have the JJ's that will work with only minimal effort.

McIntosh service guide lists those particular parts as " Specially produced for McIntosh" and they are not especially common.

(100/30-450V/500V)

The other problem with NOS can caps IMO is they are a turkey shoot. They are going to be nearly as old as the ones I have. Even reforming gives no promise that they will hold up. Caps have a shelf life, and on these parts, Or lets say, The correct parts, I am well past the shelf life span NOS or not.

Zack Engineering was the best hope because they have them custom made just for the McIntosh. But after nearly 6 weeks of waiting, Its not looking like I will be able to get them there.

I have used JJ caps in a few guitar amps, So far none have failed. They seem to be of good quality and not bad to adapt.

Trout

 

[cerrem]

You don't need the exact cap value... If it's got a bit more capacitance it actually is a good thing..also if the voltage ratting is bit higher all the merrier..
I have used these caps with McIntosh amps...
CAPACITOR, ELECTROLYTIC, 80/40/30/20 µF @ 525 VDC

C-EC80-40-30-20

Chris

 

[Trout]

FINALLY!!


I found the time to get the PS caps installed into the McIntosh.

PS Schematic

It took a bit of tinkering, I made an adapter board for the 220UF/385V (C23 & C24) because those were snap in bases. It actually worked out well.

I fabricated a piece G-10 phenolic board with eyelets so the caps snap into the board and added solder tabs and soldered everything up.
Sized the board to position both caps in the original location and mounted Via the original holes.

( Pictures Soon)

A few more wire flip flops on the 100uf/30uf caps C25A & C25B & the C26A and C26B allowed me to use a 100/100 and a 32/32.

The clamp mounts fit the original adapter plate holes on the chassis so no extra drilling required of the chassis at all in the whole project.

After about 2 hours of checking my work several times, I powered it up.
Finally no blown fuses. Very uneventful.

Now, I have 1 bug to figure out.

I made up a couple of shorting plugs for the inputs so as not to have open inputs which pick up noise.

I short the left channel, Dead silent,
The Right channel however has a mild buzz even shorted.
If it was a power supply issue, I would assume both channels would be affected.

I have not applied an audio source yet.

Note, This unit still has the original 2 wire cord. If you touch the chassis, It does reduce the buzz a little in the right channel.

I would think I need to track down the buzz then replace the cord to a standard 3 wire??
Trout

 

[SY]

The buzz is almost certainly a grounding issue, and is indeed most likely from the power supply, or more accurately, from the wiring of and to the power supply. One particular thing to pay attention to is the loop between the transformer/rectifier and the filter caps- that loop has high ripple currents, and if you return any grounds to a spot within that loop, buzz will be the result. The returns from both channels should go directly to the filter cap ground.

 

[Trout]

The buzz is almost certainly a grounding issue, and is indeed most likely from the power supply, or more accurately, from the wiring of and to the power supply. One particular thing to pay attention to is the loop between the transformer/rectifier and the filter caps- that loop has high ripple currents, and if you return any grounds to a spot within that loop, buzz will be the result. The returns from both channels should go directly to the filter cap ground.

Hmmm, I added no wire, the ground points in the PS are the same as the original. This is only showing up in the right channel.

They used the can cap tabs as several ground points, All of those are duplicated with my new cap layout. HOWEVER, I do wonder about 1 thing in particular. Looking at the schematic posted above, Parts Number C21 & C22 are .01 film caps, I did not replace those, I used the originals, 1 of which mounted directly to the can caps, the other was remotely mounted elsewhere ( totally stock)

I just played the amp via my old laptop as a source, It sounds really good, No oddities, no overheating or redplateing, Just this low level buzz similar to flourescent light fixture generated noise.

It sounds a lot like a poor ground at the input jack, I still have a few other things to try, Could even be a tube which I have not flip flopped around yet.

Its Sooo close to perfect.

Trout

 

[Trout]

Hey SY,


Your correct!!!!!

I went to take pictures to post and found a wiring issue.

When I made the adapter plate, It required that 1 cap be isolated from the chassis. I isolated both caps with the intention of adding a ground to chassis for the second cap. I stopped for dinner just after mounting the plate. Returning to the project later, I forgot a ground !!

The Darwin award of the day!! LOL

Well, while taking pictures to post, I noticed I never grounded the cap!!

original bottom layout

New Caps Top View

New Layout Bottom View

Close up of 100/100 & 32/32 Wiring

The OOOOOOPS

Welp, Im off to go add a ground ,

Thanks SY!!!

Trout

 

[SY]

Glad it worked out!

 

[Trout]

Glad it worked out!

That was it, I put the missing ground wire in, no more buzz. In fact, Sitting idle it is as noise free as any high end solid state I have ever heard.

Now I need a better source, Plugging into my old IBM thinkpads headphone jack is not exactly an ideal source, But Oh My Gosh it sounds sweet.

Thanks again for your help.
Trout

 

[Eli Duttman]

Now I need a better source, Plugging into my old IBM thinkpads headphone jack is not exactly an ideal source, But Oh My Gosh it sounds sweet.

The turntable is the next acquisition.

Enjoy the "Mac" in good health. As a H/K Cit. 2 owner, I know what a superior vintage tube amp in good repair can do.