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McIntosh - Hints and Kinks

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Yes the four Bumble bee .047 and two .1 should get replaced, the brown mylars are very good and remain. The 716 should be fine for the bumble bees, the 100uF can be 25V with no problem, I use Nichicon Muse 100uf @ 25V KZ for these two.
 
Ma-5100

Terry, you done my MC-2100, Pioneer 950, & MX-110's. My MA-5100 sounds great, is getting older as I, will bring down when can do so. You are the best..............

M.C. Price
 
Terry - another cap question. Am replacing the 1uf@63V input 'lytic coupling caps on the MC2125 and 1uf@475V film caps have been recommended. Is there any problem going that high in the voltage rating with the film caps? Thanks.
 
dewickt said:
One is on the small board, and the other is between the 2 doubler capacitors on the divider plate.
Click to expand...

The other 2 caps I cant locate are C26 and C27, at "150" according to the schematic. They're hooked up to the high voltage diodes on the schematic. I've yet to locate anything labled 150 except 2 small caps on the main board that look like ceramic caps, 150 pf but I have found them on the schematic, so I assume thats not them!:scratch2:

Thanks again,

russellc
 
C26 and C27 are the 2 twist loc can caps 150uF at 250V, these are the doubler capacitors mounted on the metal divider.

On the MC2125, a higher voltage yields a larger part, why not use a Muse ES 1uF @ 50V, it will have a smother sound than a film and be a reasonable physical size.
 
dewickt said:
C26 and C27 are the 2 twist loc can caps 150uF at 250V, these are the doubler capacitors mounted on the metal divider.

On the MC2125, a higher voltage yields a larger part, why not use a Muse ES 1uF @ 50V, it will have a smother sound than a film and be a reasonable physical size.
Click to expand...

Now that makes sense, I was looking for some tiny cap, thanks for showing me the obvious...you are the best. I'll post some pics once its done.

My power supply is a little modded. All large original caps are replaced in the power supply, but a little differently than the original. The two large caps in the "divider" are now 200 uf 250 volt sprauges, stood on top of each other
so that it forms a 100 uf 500 volt cap. this forms the first section. In the clamp by the small power supply board is a 220 uf Cerafine, which makes up the second section. The third cap section is the 20 uf 450 volt sprauge atom.

So, I guess those two cap sections are now 100 uf and 220 uf. These mods were suggested by a tech friend of mine who repaired Mcintosh for the now defunct "Accent Sound" which sold Mcintosh around here for decades....

Russellc
 
dewickt said:
On the MC2125, a higher voltage yields a larger part, why not use a Muse ES 1uF @ 50V, it will have a smother sound than a film and be a reasonable physical size.
Click to expand...
Thanks. I've got an inquiry in on the 1uf Muse, but no one seems to have them that small. Perhaps MiniSemi will find some.

Just heard back from MiniSemi - no longer carry 1uf.
 
Last edited:
Major Brain fart and retraction!

Russellc said:
Now that makes sense, I was looking for some tiny cap, thanks for showing me the obvious...you are the best. I'll post some pics once its done.

My power supply is a little modded. All large original caps are replaced in the power supply, but a little differently than the original. The two large caps in the "divider" are now 200 uf 250 volt sprauges, stood on top of each other
so that it forms a 100 uf 500 volt cap. this forms the first section.
Click to expand...


When I first got this amp, I had never seen the inside of a Mcintosh MC 225 ( or any other Mcintosh for that matter) and a friend who was also a Mcintosh repair person tagged the parts that needed replaced and gave me a bill of material to buy. I followed his advice blindly and to the letter. When I opened this amp up again and saw the two blue Sprauge 200 uf caps that were connected postive to negative, I thought I had stacked them to increase the voltage, but then Terry pointed out to me that these two caps are C 26 and C27! So actually the 200 uf Spragues replace the 150 uf units that resided there. The Cerafine replaces both C 29a, 80 uf and C 29b, 35 uf with a single 220 uf cap. The 20 uf 450 volt Atom cap replaces the final cap, originally 15 uf.

Good grief!

Russellc
 
Got the bumble bees replaced, resistors?

Now that I've installed the .047 and .1 replacements, ( still waiting for the .01) I got to wondering about the resistors on the main board. they appear to be in 2 sizes, I assume the smaller are 1/2 watt and the larger are 1 watt?

If not, what values do we have here? I notice on the schematic a few are to be 1% match. What are good reliable and good sounding replacements? I know some use Allen-Brady carbon comp resistors, but I here stories about drift.... I just want something reliable that sounds good in the tradition of this amp.

Thanks for any advice or suggestions,

Russellc
 
Nichicaon Muse are excellent. A couple of sources are Handmade Audio and Michael Percy Audio. You can also tell them the application and ask for suggestions.
 
Ok, I got it all back together. The two large power supply caps are Sprague
200uf 2 250 volts, screw terminals. The .01 cap associated with them was replaced with a sprague 716 SBE .01 600 volt film cap. The other .01 cap, located on the small power supply board was replaced with the same Sprgue 716 film cap.

The bias cap was replaced with a sprague Atom, 20 uf @ 450 volts. The 33k resistor was replaced with a visay metal film 1/2 watt. The 30K resistor next to it was also replaced with the same 33k resistor, to drop the increased bias voltage caused buy the lessened voltage drop of the 1N4004 diode that replaced the selenium bias rectifier. The .047 bumble bee caps on the board were replaced with Sprague SBE 716 .047 600 volt caps. The .47 caps were replaced with Sprague 730P .47 at 100 volts. The 2 cathode bypass caps were replaced with Sprgue Atom 100 uf 100 volt electrolytic capacitors. The volume controls were replaced with audio taper pots of the same values as the original.
The bumble bees across them were replaced with Sprague SBE 716 .1, 600 volt caps.

Initial fire up via variac, brought the plates up to 390 volts. pin 8. Once stabilized and having stared at the output tubes for red plate the entire time,
I measured the bias voltage at a perfect -21 volts.

Its breaking in now, powering the Indignias. Nice. Thanks to all who threw in the info, especially Terry and Dsloaf, with out who's help this may have been impossible. Hopefully, It'll be ready to go for some time. Most all of the parts used were of industrial strength, like the originals of the time.

Thanks to all for the help,

Russellc
 
LotusFool said:
After reading this artical;
http://www.audioasylum.com/scripts/d...oes-tubes.html
I am considering replacing my 12AX7 with a 5751 on my MC225. Has anyone (Terry) tried this, and what did you think.
I entered this question on the tube page and was told the gain would be less with the 5751, but otherwise, nobody thought it would be a problem for my MC225.

Thanks
Gary
Click to expand...

I have, and it worked fine. Ive tried GE 5751 5 star, RCA Command series, RCA black plates with triple mica, and Raytheon black plate 5751s. Oddly, of those and several other 12ax7A tubes, I still seem to keep coming back to the Telefunken smooth plate. Odd, as I generally dont care for ther sound of that tube!

by the way, the link doesnt work.

Russellc
 
I am using the Telefunken smooth plate now, maybe I won't bother after reading your experience. Sorry about the link.

Gary
 
I am careful about the first stage since it where the global feedback is inserted at the cathode, if the gain drops to low the distortion may go up, though not normally enough to hear.
 
dewickt said:
I am careful about the first stage since it where the global feedback is inserted at the cathode, if the gain drops to low the distortion may go up, though not normally enough to hear.
Click to expand...

Which tubes do you recommend for this first position? Tonight I'm trying a Tungsol 12AX7A. I realize I've replaced a lot of parts here, and while I generally findnew builds to sound a little wirey until run awhile, I'm wondering if some of those caps need to be a bit mellower type perhaps? Any suggestions greatly appreciated.

russellc
 
LotusFool said:
After reading this artical;
http://www.audioasylum.com/scripts/d...oes-tubes.html
I am considering replacing my 12AX7 with a 5751 on my MC225. Has anyone (Terry) tried this, and what did you think.
I entered this question on the tube page and was told the gain would be less with the 5751, but otherwise, nobody thought it would be a problem for my MC225.

Thanks
Gary
Click to expand...

Say, last night I did a little swapping of the 12ax7a and tried the Tungstram
12ax7a. short story, definate new favorite over the Tele flat plate. The wirey sound I was attributing to the poly prop film and foil caps I installed is now gone! Tonight, I'm trying a batch of 5751 tubes. But, if Terry said it would cause a little more distortion, you can bet your last dollar it will. He knows his stuff and has forgotten more than I'll ever know, thats for sure!

thanks again Terry!

Russellc
 
Yeah by all means keep us posted for your results. I'm using a tele smooth plate and I'm all for trying something different.

gary
 
I'll post some pics of these tubes once I get home, but here's the lineup from last night.

Thinking the one Telefunken may be a little tired or getting microphonic, I tried another. Basically the same results, a little more full sound at higher volumes, still somewhat dry.

Next, the 5751. I tried an older RCA Command series, a newer RCA Command series, and a A GE 5 star. All sounded good, not as much involvement. Very similar signature,, nice bass, not quite the dynamics of the 12ax7a tubes in the same position. Seems the 5 star was the best of the lot. surprising, as the pre has RCA command series, and I really thought that would be the one.

Going back to the Tungsram 12ax7a, it was the clear winner in my opinion.
Full and rich, great dynamics. Got a few more 12ax7as, but the Tungsram seems to be the winner for me.

russellc
 
dewickt said:
MC2205 has a bias adjustment on the driver board, correctly set the heatsinks will get slightly warm at idle (no output). The bias setting procedure requires an AC amp meter in the AC line, procedure is described in the service manual.
Click to expand...
Getting ready to do some work on my MC2125 and it uses a similar bias setting adjustment. It would seem to me to be simpler and more accurate to be able to measure the voltage across a resistor for this rather than a current measurement in the AC line. Am I correct?
 
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