[h=Introduction]%1[/h]
The McIntosh MC250 is one of the iconic amps with a nice
warm sound.
[h=Documentation]%1[/h]
Link to the Owners Manual.
http://www.berners.ch/McIntosh/Downloads/MC250_own.pdf
Here is a link for the Input board:
http://www.diyaudio.com/forums/atta...-replacement-mcintosh_mc250_input_section.png
[h=Pics ]%1[/h]
http://www.diyaudio.com/forums/soli...elp-my-mcintosh-mc250-please.html#post3345059
[h=Recommendations]%1[/h]
Shown is the underside of the MC250. Highlighted are
two of the Mylar caps, they generally don't need changing
but the electrolytics should be replaced.
Image from ahankinson:
http://www.diyaudio.com/forums/atta...tosh-mc250-capacitor-replacement-imag0393.jpg
Caps used by ahankinson include the following:
No, I didn't want to touch too much, so I just replaced the caps. Here's the digikey parts numbers I used:
4000PHCT-ND
CAP ALUM 470UF 6.3V 20% AXIAL
CUST REF #: C11, C12
493-3190-ND
CAP ALUM 100UF 25V 20% RADIAL
CUST REF #: C51, C52
493-10824-1-ND
CAP ALUM 10UF 25V 20% RADIAL
CUST REF #: C53, C54
493-13368-ND
CAP ALUM 1000UF 25V 20% AXIAL
CUST REF #: C55, C56
http://www.digikey.com/short/7dt04n
Check the electrolytic capacitors on the input board they have
a tendency to open. --anatech
Also trace the audio signal through the amp using a signal generator
at the input and follow it through the amp comparing left and right
channels.
Use 1Vp-p signal and adjust for no clipping. Find the problem
area.
Note the amp clips at about .5Vrms
[h= Pictures]%1[/h]
Trying to find the best images with thumbnail to click then full size.
Email and IM pasted
http://smg.photobucket.com/user/TheAmpNerd/media/McIntosh/03.MC250BoardTest3_zpskhos9mgn.jpg.html
Email and IM (linked)
http://smg.photobucket.com/user/TheAmpNerd/media/McIntosh/03.MC250BoardTest3_zpskhos9mgn.jpg.html
Direct (pic paste):
Direct Paste:
http://img.photobucket.com/albums/v209/TheAmpNerd/McIntosh/03.MC250BoardTest3_zpskhos9mgn.jpg
Direct Linked:
http://img.photobucket.com/albums/v209/TheAmpNerd/McIntosh/03.MC250BoardTest3_zpskhos9mgn.jpg
HTML Pasted
[h=Problems]%1[/h]
Problems are trying to find the correct transistors. If if i you have a nice
amp we don't want to drill out the heat sink to fit the larger T03 parts in place
of the smaller TO-66 parts.
ORIGINAL PARTS
TO-66..Vceo....HFe....Idss....TYPE
NPN.....120........65.,...50.....2N3738 x 2ea Drives the following:
NPN......90........25....150.....2N3767 x 2ea paired with T03
PNP.......90.........25....150.....2N3741 x 2ea paired with T03
PAIRED OUTPUT
NPN.....80....30-90.......5A.....2N5303 X 4 paired with ea TO-66
REPLACEMENTS CONSIDERED --CAUTION--
(Might oscillate and fry transformers)
Output each paired with TO-66
T03 x 4ea
NPN BJT 16A 250V 250W MJ21194 (on Semi)
-- END CAUTION --
The amp is nice enough to try and find and use the TO66 devices.
Related, here is a table:
Input Board
Also looking for the CH sized output capacitors too; 9300uF, 50V
1.125 (24mm) screw center caps.
Approx 2-1/2 x 2-1/2 to 3 inches .
Here is link to my search to buy parts:
http://www.diyaudio.com/forums/swap...2n3741-66-transistors-others.html#post4321912
[h=Other]%1[/h]
Support
The McIntosh MC250 is one of the iconic amps with a nice
warm sound.
[h=Documentation]%1[/h]
Link to the Owners Manual.
http://www.berners.ch/McIntosh/Downloads/MC250_own.pdf
Here is a link for the Input board:
http://www.diyaudio.com/forums/atta...-replacement-mcintosh_mc250_input_section.png
[h=Pics ]%1[/h]
http://www.diyaudio.com/forums/soli...elp-my-mcintosh-mc250-please.html#post3345059
[h=Recommendations]%1[/h]
Shown is the underside of the MC250. Highlighted are
two of the Mylar caps, they generally don't need changing
but the electrolytics should be replaced.
Image from ahankinson:
http://www.diyaudio.com/forums/atta...tosh-mc250-capacitor-replacement-imag0393.jpg
Caps used by ahankinson include the following:
No, I didn't want to touch too much, so I just replaced the caps. Here's the digikey parts numbers I used:
4000PHCT-ND
CAP ALUM 470UF 6.3V 20% AXIAL
CUST REF #: C11, C12
493-3190-ND
CAP ALUM 100UF 25V 20% RADIAL
CUST REF #: C51, C52
493-10824-1-ND
CAP ALUM 10UF 25V 20% RADIAL
CUST REF #: C53, C54
493-13368-ND
CAP ALUM 1000UF 25V 20% AXIAL
CUST REF #: C55, C56
http://www.digikey.com/short/7dt04n
Check the electrolytic capacitors on the input board they have
a tendency to open. --anatech
Also trace the audio signal through the amp using a signal generator
at the input and follow it through the amp comparing left and right
channels.
Use 1Vp-p signal and adjust for no clipping. Find the problem
area.
Note the amp clips at about .5Vrms
[h= Pictures]%1[/h]
Trying to find the best images with thumbnail to click then full size.
Email and IM pasted
http://smg.photobucket.com/user/TheAmpNerd/media/McIntosh/03.MC250BoardTest3_zpskhos9mgn.jpg.html
Email and IM (linked)
http://smg.photobucket.com/user/TheAmpNerd/media/McIntosh/03.MC250BoardTest3_zpskhos9mgn.jpg.html
Direct (pic paste):
An externally hosted image should be here but it was not working when we last tested it.
Direct Paste:
http://img.photobucket.com/albums/v209/TheAmpNerd/McIntosh/03.MC250BoardTest3_zpskhos9mgn.jpg
Direct Linked:
http://img.photobucket.com/albums/v209/TheAmpNerd/McIntosh/03.MC250BoardTest3_zpskhos9mgn.jpg
HTML Pasted
[h=Problems]%1[/h]
Problems are trying to find the correct transistors. If if i you have a nice
amp we don't want to drill out the heat sink to fit the larger T03 parts in place
of the smaller TO-66 parts.
ORIGINAL PARTS
TO-66..Vceo....HFe....Idss....TYPE
NPN.....120........65.,...50.....2N3738 x 2ea Drives the following:
NPN......90........25....150.....2N3767 x 2ea paired with T03
PNP.......90.........25....150.....2N3741 x 2ea paired with T03
PAIRED OUTPUT
NPN.....80....30-90.......5A.....2N5303 X 4 paired with ea TO-66
REPLACEMENTS CONSIDERED --CAUTION--
(Might oscillate and fry transformers)
Output each paired with TO-66
T03 x 4ea
NPN BJT 16A 250V 250W MJ21194 (on Semi)
-- END CAUTION --
The amp is nice enough to try and find and use the TO66 devices.
Related, here is a table:
Input Board
Q1 NpN
B-E
r OL
b .64
B-E
r OL
b .64
C-E
r OL
r OL
b .62
Q3 NpN
Q3 NpN
B-E
r OL
b .64
B-E
r OL
b .3 rising.
Q5 - PnP
Q5 - PnP
B-E
r OL
b 2.9
C-E
r OL
b 2.9 rising
Q2 - NpN
Q2 - NpN
B-E
r OL
b .64
C-E
r OL
b.29
Q4- NpN
Q4- NpN
B-E
r OL
b .63
C-E
r .8
b OL
Q6 - PnP
Q6 - PnP
B-E
r .65
b 2.9
r 2.9 to OL
b 1.9 ++ 2/9
Also looking for the CH sized output capacitors too; 9300uF, 50V
1.125 (24mm) screw center caps.
Approx 2-1/2 x 2-1/2 to 3 inches .
Here is link to my search to buy parts:
http://www.diyaudio.com/forums/swap...2n3741-66-transistors-others.html#post4321912
[h=Other]%1[/h]
Support
Will investigate using the following for the MC250/MC2505
and have to identify location of the capacitors in this MC250/2505
http://www.diyaudio.com/forums/solid-state/272315-new-me-mcintosh-mc2205.html#post4281027
and have to identify location of the capacitors in this MC250/2505
http://www.diyaudio.com/forums/solid-state/272315-new-me-mcintosh-mc2205.html#post4281027
Last edited:
Description from KISS here:
http://www.diyaudio.com/forums/solid-state/93240-vintage-mcintosh-mc250-help-needed.html#post1098943
http://www.diyaudio.com/forums/solid-state/93240-vintage-mcintosh-mc250-help-needed.html#post1098943
Discussion of transistors is attached here:
http://www.diyaudio.com/forums/solid-state/2490-help-needed-mcintosh-mc2500.html#post19661
http://www.diyaudio.com/forums/solid-state/2490-help-needed-mcintosh-mc2500.html#post19661
Discussion of the capacitors used:
http://www.diyaudio.com/forums/soli...-mc250-capacitor-replacement.html#post3795314
http://www.diyaudio.com/forums/soli...-mc250-capacitor-replacement.html#post3795314
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