McIntosh MC250

[p2pAmps]

Any of you boys know where I can source some parts for my old McIntosh MC250 amp? 

This is what I need to start with:
NPN Transistor 070-022
NPN Transistor 132-021
Rectifier Diode 132-515

Service Manual

https://www.dropbox.com/s/qps8dmv24f758ql/MC250_ser.pdf?dl=0




 

[pompeiisneaks]

according to the service manual:

http://www.tubebooks.org/file_downloads/McIntosh/MC250_ser.pdf

the first is a diode rectifier not an NPN transistor, according to the site, but man I definitely can't seem to find any real part numbers that relate anywhere or NOS stuff on Ebay for it either... You can probably look at the schematic in there and look for the type of transistor needed and find a comparable one, but I think those old transistors look germanium instead of the newer silicon, but then that schematic says they're Si ones. 

Hopefully that's the right service manual, at least it should help narrow down the voltage ranges etc for the specific failed parts.

~Phil

[pompeiisneaks]

Oh looks like you posted the link to the schematic too heh. 

~Phil

[pompeiisneaks]

oh my google fu seems to have finally landed on something:

http://www.diyaudio.com/forums/solid-state/272524-mcintosh-mc250-repair-upgrade.html

This seems to show modern replacement named transistors for the repairs you need

(I also realized you just swapped the names, you did list two transistors and a diode but just put the names before the wrong ones, the 132- are all transistors and the 070 are all diodes).

so per that link, your missing



and the 132-021 should be a 2N3569:

http://www.ebay.com/sch/i.html?_nkw=2n3569+transistor&clk_rvr_id=1144906316620&gclid=Cj0KEQiAnIPDBRC7t5zJs4uQu5UBEiQA7u5Ne6VSRoGDmWMRvVdfpsES6LuaJCAV39xg7fkz1ncdUA8aApjR8P8HAQ&geo_id=10232&MT_ID=69&crlp=167399314520_1647&rlsatarget=kwd-39696127454&keyword=2n3569+transistor&treatment_id=7&poi=&adpos=1t1&device=c&crdt=0&ul_noapp=true

and the 132-515 should be a TO-66:

http://www.ebay.com/sch/i.html?_odkw=2n3569+transistor&adpos=1t1&gclid=Cj0KEQiAnIPDBRC7t5zJs4uQu5UBEiQA7u5Ne6VSRoGDmWMRvVdfpsES6LuaJCAV39xg7fkz1ncdUA8aApjR8P8HAQ&ul_noapp=true&geo_id=10232&MT_ID=69&crlp=167399314520_1647&keyword=2n3569+transistor&rlsatarget=kwd-39696127454&device=c&crdt=0&treatment_id=7&clk_rvr_id=1144906316620&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR1.TRC0.A0.H0.XTO-66+transistor.TRS0&_nkw=TO-66+transistor&_sacat=0

As for the diode bridge I'd guess just going massively over spec rated should work, like 1.4kV diodes to be sure. 

Probably overkill, but that's the point here, never have to replace those again :)

~Phil

[Ritchie200]

Mike,


Looking at some of the McIntosh forums, it appears that some of the schematics listed McIntosh numbers, not necessarily Motorola numbers (for example).  I did run across this posting.  It is a few years old but maybe there is still support and they can give you replacement information? 


Hi everyone. McIntosh doesn't supply general parts, i.e. resistors, capacitors as well as any parts that can be found at the various distributors like Newark, Allied, Digi-Key or Mouser. Unique parts can be obtained from the Factory Parts department at (800) 538-6576. Ask for either Brian or Gail. In many cases they will require the McIntosh part number. The Factory and the 3 Restoration centers will not recommend or support any type of modifications, unless they are from the Factory.
Mark
McIntosh Factory Restoration Facility
McIntosh@AbSoundLabs.Com


Good luck!
Jim

[p2pAmps]

oh my google fu seems to have finally landed on something:

http://www.diyaudio.com/forums/solid-state/272524-mcintosh-mc250-repair-upgrade.html

This seems to show modern replacement named transistors for the repairs you need

(I also realized you just swapped the names, you did list two transistors and a diode but just put the names before the wrong ones, the 132- are all transistors and the 070 are all diodes).

so per that link, your missing



and the 132-021 should be a 2N3569:

http://www.ebay.com/sch/i.html?_nkw=2n3569+transistor&clk_rvr_id=1144906316620&gclid=Cj0KEQiAnIPDBRC7t5zJs4uQu5UBEiQA7u5Ne6VSRoGDmWMRvVdfpsES6LuaJCAV39xg7fkz1ncdUA8aApjR8P8HAQ&geo_id=10232&MT_ID=69&crlp=167399314520_1647&rlsatarget=kwd-39696127454&keyword=2n3569+transistor&treatment_id=7&poi=&adpos=1t1&device=c&crdt=0&ul_noapp=true

and the 132-515 should be a TO-66:

http://www.ebay.com/sch/i.html?_odkw=2n3569+transistor&adpos=1t1&gclid=Cj0KEQiAnIPDBRC7t5zJs4uQu5UBEiQA7u5Ne6VSRoGDmWMRvVdfpsES6LuaJCAV39xg7fkz1ncdUA8aApjR8P8HAQ&ul_noapp=true&geo_id=10232&MT_ID=69&crlp=167399314520_1647&keyword=2n3569+transistor&rlsatarget=kwd-39696127454&device=c&crdt=0&treatment_id=7&clk_rvr_id=1144906316620&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR1.TRC0.A0.H0.XTO-66+transistor.TRS0&_nkw=TO-66+transistor&_sacat=0

As for the diode bridge I'd guess just going massively over spec rated should work, like 1.4kV diodes to be sure. 

Probably overkill, but that's the point here, never have to replace those again :)

~Phil

Great, Thanks Phil.  Got the two parts ordered, now on to the Diode. 

I'm actually getting ready to sell both my McIntosh MC250s as I am building a Dynaco ST120 which is all I need.  I nearly went for two mono blocks but just hard to justify the cash when the 120 is so dang sweet...  I'll be running 4 - KT120s in her!

[p2pAmps]

Mike,


Looking at some of the McIntosh forums, it appears that some of the schematics listed McIntosh numbers, not necessarily Motorola numbers (for example).  I did run across this posting.  It is a few years old but maybe there is still support and they can give you replacement information? 


Hi everyone. McIntosh doesn't supply general parts, i.e. resistors, capacitors as well as any parts that can be found at the various distributors like Newark, Allied, Digi-Key or Mouser. Unique parts can be obtained from the Factory Parts department at (800) 538-6576. Ask for either Brian or Gail. In many cases they will require the McIntosh part number. The Factory and the 3 Restoration centers will not recommend or support any type of modifications, unless they are from the Factory.
Mark
McIntosh Factory Restoration Facility
McIntosh@AbSoundLabs.Com


Good luck!
Jim

Thanks Jim,

Yeah I tried calling them this morning but just got the ole VM.  I figure after new years they will all be back. 

I'm not all that great at fixing these things so Im using what I know about tube amps and just doing my checks.  That board for the left channel took a pretty serious hit so after I replace all the burned up parts I will see where that leads me.  I may have to get one you real wizards to repair this thing if I strike out... LOL...

Cheers,

[pompeiisneaks]

Nice, that may be a next project for me too, some kind of HiFi stereo Tube amp.   

Different world though, I've been lurking on some FB groups more focuses on that and its quite different.

~Phil

[p2pAmps]

Nice, that may be a next project for me too, some kind of HiFi stereo Tube amp.   

Different world though, I've been lurking on some FB groups more focuses on that and its quite different.

~Phil

I'm going to start with a VTA120 amp

http://www.tubes4hifi.com/bob.htm

~mike

[pompeiisneaks]

Very nice, that's a little cheaper than some of the bottlehead kits I had thought  about and a lot of power ;)

~Phil

[p2pAmps]

Very nice, that's a little cheaper than some of the bottlehead kits I had thought  about and a lot of power ;)

~Phil

These amps have huge good reviews by guys who are totally into hifi.  I was close to building 2 Mono blocks but just don't need that much power

[PRR]

D1 D2 (not diode bridges but reference diodes) are critical to set up output stage bias.

If I accept the volt numbers on the sheet, it is about 1.5V. Which is not any integer number of typical 0.6V diode drops.

As a get-it-running hack, two 1N400x in series pointing down will get the output stage idle bias near conduction, and on the safe (cool) side of the goal. A short will run but be some rough on small signals.

That's all that's in a early Mac tranny amp?? Oh, I see there's an input section also. Still this is very minimalist. (Compare to contemporary early Crown DC-300.)

The output transistors are seriously over-worked and they don't make them like that any more. Replacements may be different enough to justify a for-purpose D1 D2 instead of the old spec.

[p2pAmps]

McIntosh Labs had my parts!  I'm happy for now and I will be happier once I actually fix it.  No news here I'm not a hifi tech so I'm flying by the seat of my pants here. 

[sluckey]

It's been a long, long time since I worked on that kind of equipment. But one thing I remember, it's rare that only one transistor and burned diode is all that's wrong. The power amp is all direct coupled and it's common for several transistors to be shorted. And even worse, if you leave one shorted transistor in that channel you'll probably destroy the new one(s) quicker than you can turn it on and right back off.

My point is check every transistor in the power amp channel that failed. Not just the ones on the heat sink. Check every transistor back to the input of the power amp board. It's a pain in the ass, but doing so can save you a bunch of time, money, and frustration.

A simple front/back ratio check with an analog ohm meter is sufficient to adequately check those transistors. But you have to pull them out of the circuit.

[p2pAmps]

It's been a long, long time since I worked on that kind of equipment. But one thing I remember, it's rare that only one transistor and burned diode is all that's wrong. The power amp is all direct coupled and it's common for several transistors to be shorted. And even worse, if you leave one shorted transistor in that channel you'll probably destroy the new one(s) quicker than you can turn it on and right back off.

My point is check every transistor in the power amp channel that failed. Not just the ones on the heat sink. Check every transistor back to the input of the power amp board. It's a pain in the ass, but doing so can save you a bunch of time, money, and frustration.

A simple front/back ratio check with an analog ohm meter is sufficient to adequately check those transistors. But you have to pull them out of the circuit.

Yes it is a PITA but everything in this amp is fairly easy to get to.  I ordered extras too incase I find another open transistor.  I already have a stock of Allen Bradley resistors so I'm good there. 

Soon as I finish this and a Twin Reverb gut job I'm going to start my VTA St120 Dynaco with KT120s.  Can't wait to hear that beast

[p2pAmps]

For anyone who might be working on a McIntosh


Input PCB
Q1,Q2 NPN Transistor 3 Pin 132-054 2N5210 50 200 600 100uA
Q3, Q4 NPN Transistor 3 Pin 132-054 2N5210 50 200 600 100uA
Q5, Q6 PNP Transistor 3 Pin 132-056 2N2087 50 250 800 100uA


OUTPUT DRIVER PCB
Q7, Q8 PNP Transistor TO-92 13C 132-056 2N2087 50 250 800 100uA
Q9, Q10 PNP Transistor TO-92 13C 132-056 2N2087 50 250 800 100uA
Q15, Q16 NPN Transistor 3 Pin 132-021 2N3569 40 90 30
Q17, Q18 PNP Transistor 3 Pin 132-032 2N3645 60 50 100

OUTPUT DRIVERs PCB
Q11, Q12 NPN Transistor TO-66 132-515 132-028 2N3738 120 65 50

OUTPUT Transistors (on heatsink) TO-66
Q19, Q20 NPN Transistor Output TO-66 132-524 132-023 2N3767 90 25 150
Q21, Q22 PNP Transistor Output TO-66 132-530 132-023 2N3767 90 25 150


OUTPUT Transistors (on heatsink) TO-3
Q23, Q24 NPN Transistor Output 132-070 2N5303 80 30 90 5A
Q25, Q26 NPN Transistor Output 132-070 2N5303 80 30 90 5A