• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

MC2125 power transistors

C

clem

New Member
Would anyone know the proper replacement transistors for this unit ?

Symbol Q227-228-229-230-237-232-233-234-237-238-Q240

Several transistors were marked Motorola 132164-7813 and 132165-7813
and a Hong Kong marked/made F744-152 & F805-151

MC Part #
132-151
132-152
132-164
132-165


I have at least one transistor blown and figure I better do all of them.

I rescued this item from the recycle/trash area as it was destined for scrap. It cleaned up nice so far and has needed several D308 Si rectifier/diodes and all the lamps..

My first Mcintosh, I hope to match it to a Vintage Empire Turntable and a Denon preamp and some old ohm speakers. We will see..

Thanks for your time
 
Register to hide this ad
Welcome to AK. The MC2125 is a terrific amp. While you are in there you should replace all the small-signal coupling caps, as well. There are several good threads on recapping this era amp in this (McIntosh) forum. Especially good are Gregory's MC2205 recap threads with many photo's that show his work. The MC2125 is quite similar. For a cross reference on that transistor, send a PM to AK member EchoWars. EW usually hangs out over in the Vintage Solid-State forum or just look him up in the members list.
 
clem said:
I have at least one transistor blown and figure I better do all of them.
Click to expand...

Yes, if any of the outputs are shorted, replace all of them with the newest types, don't intermix older and newer or nasty things can happen.

I also recommend replacing the drivers and the bias transistors at the same time, again using the newest parts. Many techs also recommend replacing the differential pair in older Mac amps regardless of the condition of the rest of the unit as a precaution, these tend to get noisy or intermittent as they age.

A fine amp once up and running properly; it's hard to believe someone would actually trash one.
 
Probably the best choices are the On-Semi MJ15003 (NPN) and rhe MJ15004 (PNP). As far as crossing to your numbers, the manual should tell you which is which (NPN vs PNP).

Buy only from a reputable supplier, such as Mouser or Digikey.
 
Thank You Echo Wars,

I had considerd the "On-Semi" branded power transistor as I see they took over the Motorola business. I will take you advise on that for sure.

However why did macintosh use two hong kong made trasistors ? Are they diffrent for a perticular reason ? One is a NPN and the other a PNP..Hong Kong marked/made F744-152 & F805-151

Can I use the On-Semi MJ15003 (NPN) and the MJ15004 (PNP)in place of the hong kong made transistors and the motorola transistors ?

Thanks for you help, as I have not done much bench level repair in 25 years, but I amenjoying this project so far.
 
The McIntosh amps of this age need a restoration, not just a repair.

When you posted yesterday I was putting togather a list of parts needed to restore a Mc2125 that was..... made illegitiment by a tech cutting corners to fix it quick. (heatsink thermistor burned, welded relay contact).

You have a schematic?? 151 and 152 are drivers 164 and 165 are a pair of the 3 or 4 different outputs they used over the long life of this and the MC-2205.

Failing diodes would concern me, which ones? Lots of caps are suspect as well as low level transistors.
 
My cross-reference shows MJ15020 and MJ15021 as the outputs that I have gotten from the parts department at McIntosh.
 
Thanks Dewickt

Do you recomend MJ15020 and MJ15021 for all the power transistors? Or just the hong kong

MC Part #
132-151
132-152
132-164
132-165



Motorola 132164-7813 and 132165-7813
and
Hong Kong marked/made F744-152 & F805-151
 
I have seen D308-D302-D303 fail . Mcintosh part number 070-031.

I am replacing them with IN5395GP RECTIFIERS by GENERAL INSTRUMENT 1.50 AMPS 400 VOLTS.

Is this correct ?
 
So the amp uses TO-3 drivers? The MJ15020 & MJ15021 will do fine (current capability too low for final outputs, and bandwidth a bit too high). I still recommend the MJ15003 & MJ15004 for final outputs.

Clem, it is important for you to learn enough to be able to converse on a basic level...in this case, to learn which transistors are the final output devices, and which are the drivers for the outputs.

(I got your PM. Better to reply here.)
 
The part numbers and schematic numbers that op listed are as follows, 12 in total.

132-151 - pnp, Q227/228
132-152 - npn Q229/230
132-164 - npn Q231/232/233/234
132-165 - pnp Q237/238/239/240

The four different part numbers are probably where the confusion is coming from. My x ref doesn't list the 132-164/5 so I can't tell what the difference is.

Murray
 
Yes the drivers are the 15020 and 15021 with the outputs the 15003 and 15004, if you use the 15003 and 15004 as drivers you will get a parasitic oscillation that varies with output power, I found out the hard way...
 
I had these crosses ready to post under restoration/repair but it got lost. According to my semi data from 90 the drivers 132-151 xto 132-230= MJ15019 now MJ15025. 132-152 xto 132-229 = MJ15018 now MJ15024.

The outputs could be 164/188 or 165/189 but all cross to MJ15003 and 04.

If those diodes failed the caps on the power supply board gotta be toast.
 
You must log in or register to reply here.
Back
Top Bottom