The McIntosh MC250 is one of the iconic amps with a nice
warm sound.

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/attac...ut_section.png

http://www.diyaudio.com/forums/solid...ml#post3345059

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/attac...t-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

Trying to find the best images with thumbnail to click then full size.
Email and IM pasted
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Email and IM (linked)
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Direct Paste:
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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-...ml#post4321912

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