McIntosh MC2105 question

[AngelAT]

Hello AKs,

I am a SS units repair hobbyist- lately getting aquatinted with the pleasure a MAC can provide.

Six months ago I bought my first MAC - a C29 preamp with a defect- someone has done a lousy job converting her from 110v to 240v. With the help of you guys (IvoCRo, c_dk and Patrice) and a lot of reading I managed to fix her the proper way and am currently enjoying the sound. Since then I started looking for an amp - MC2105. The other day I finally got one! Not the best looking and with some issues...

Now to my question: the guy I bought the MC2105 from claims the unit is 110v. At the back there is no 220v sticker. Checking the schematics this unit is easier for converting to 230v compared to my C29. I found out that blk/red should be connected to blk/yel. This is what I see inside



To me this looks like blk with a resistor and blk/red to blk/yel through the resistor. Furthermore, the fuse is 250v (but 5A?) and there is the plug type...

And I can tell that someone has been inside.

I just do not want to plug this MAC into the mains. And I didn’t have a variac.

What do you guys think?

Thanks in advance!

 

[c_dk]

Patrice has all the experience here with the correct way to do conversions. He has been a official voltage converter in Paris for decades.

But as a side note those discs appear to be thermistors that soften the turn on surge.

 

[AngelAT]

c_dk, thanks for the prompt reply!
I hope you guys will support me in this project - after the conversion I will have to go through the unit. Seller said that one channel is not working, the other is buzzing.
Looking forward!

 

[clinic-audio]

Hello AngelAT

I can confirm that you can connect your amplifier to 220V without any risk at all
But I will replace the power cord because the plug is a molded type and diameter of this power cord (ordinary type) is not big enough to my point of view !

The both thermistors are original and good type for 240V use

 

[c_dk]

Patrice,

Is there a way to confirm the "polarity" of the leads to properly connect them in series?

Do you use just one new NTC thermistor or the two originals?

 

[AngelAT]

Hello AngelAT

I can confirm that you can connect your amplifier to 220V without any risk at all
But I will replace the power cord because the plug is a molded type and diameter of this power cord (ordinary type) is not big enough to my point of view !

The both thermistors are original and good type for 240V use

Hello Patrice,

Thank you for the confirmation!
The seller kept repeating that it was a 110v unit...
Already changed the fuse to 2.5A/250v.
Will change the cord and will also add a sticker at the back for 220v.

Stay healthy and safe during these strange times!

 

[clinic-audio]

Patrice,

Is there a way to confirm the "polarity" of the leads to properly connect them in series?

Do you use just one new NTC thermistor or the two originals?

Hello Chris
the way to confirm polarity of the leads (good question ! ) is to follow official factory conversion instructions . If you don't you will be "out of phase" and you know the consequences ......

These instructions are in hands of official distributors and factory (of course)

Regarding thermistors : replacing original is not necessary ! here, they are original type

 

[clinic-audio]

Hello Patrice,

Stay healthy and safe during these strange times!

thank you !

you too

 

[AngelAT]

Hello,

I quick update as to what I have done so far:

- The MC2105 is 220V, I have replaced the power cord and the main fuse.
- Furthermore, when testing with a DBT there was a short (bright bulb) when the speakers were on with and without the driver boards. It came to be a problem at the left channel - 3 of the end transistors were gone as well as some of the resistors at the heat sink (0.33 and 0.56 Ohms) so I replaced the defective ones with MJ15003 and all the WW resistors. And there was no short.
- But with the driver boards there was again a bright bulb (short) so I found it was the board of the left channel. Q107 and Q111, 113 were gone together with R129. Replaced Q107, 108, 109, 110 with MPSA05 and MPSA 55 and Q111,112, 113, 114 with 2N5320 and 2N5322. Q101, 102, 103, 104 were ok. Replaced the electrolytic caps with axial Vishays. Furthermore, removed C123, 124 and replaced R119,120 with 18 Ohms (this is as per the recommended mod). But for your information the heatsink at Mouser (532-322400B00) is too small, so I kept the original heatsinks. And as expected no bright bulb.
- Then replaced all end transistors with MJ15003 and also all WW resistors.
- Replaced the electrolytic caps at the input board again with axial Vishays.
- Replaced the speaker terminals as they were in not good condition. Used Mouser 504-TB100-04B, but be aware that some drilling has to done on these.
- Cleaned the pots.
- Did the meter calibration.
- Replaced some of the face plate lamps.
- Painted the bottom and added feet, because the Mac came without.

And the MC2105 is making me happy with its sound.

I have two questions, guys:

- When I power the Mac off the sound fades for 5-6 secs and then stops. I am aware that there is no relay, but is this normal?
- Most probably at some point in time one of the decibel meters has been replaced and now there is a difference in the whiteness of the two. What ideas can you suggest to fix this, because I do not like it?

Stay safe!

 

[damacman]

Sound after power off is normal as the caps are drained. My MC2300s do the same.

 

[AngelAT]

Sound after power off is normal as the caps are drained. My MC2300s do the same.

Thanks, damacman!

 

[AngelAT]

A quick update!

I think now all came to its place.
After some time, I can say that I am now happy with my McIntosh 2105. I ordered a new glass faceplate because the original one was far from good.
A big THANK YOU! to Patrice for providing me with new db meter plates since mine were with different discolouration.

So after 7 months the McIntosh 2105 which I bought in a pretty beaten-up condition - without feet, lots of scratches, extremely dirty, etc is now proudly sitting next to my other units.


A funny fact is that the guy I bought her from kept repeating that the unit is 110V. And it came out that someone has changed the power transformer voltage to 220V.
One channel was gone and I replaced all end transistors for both channels. Furthermore I recapped the whole unit (with exception of the tripple capacitor). Cleaned her as much as possible, repainted the bottom, put some new feet.
As already mentioned replaced the faceplate and the db indicator scales (thanks Patrice!).



Since the light at the meters originally was a bit blurry, I replaced the incandescent lights with LEDs. Furthermore, added some foil to further increase the light.



...and I got my Christmas present a bit early.
Now I enjoy the magnificent sound this bijou produces!



BTW
I still have the two old discoloured pointer scales and the glass faceplate. What should I do with them?