McIntosh output transistors

Discussion in 'McIntosh Audio' started by c_dk, Nov 11, 2013.

  1. c_dk

    c_dk Addicted Member

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    In another thread Patrice and I discussed suspect outputs in a client's MC7270 that was on my bench.

    Sent pictures to Terry.....he does not know what they are.....talked to my last contact in Mac engineering and he says they are not stock....even with the correct Mac part number.

    Looks like there are others in the other heatsinks.....any idea who might be misrepresenting these as Mac parts?

    Drivers are correct.....1 rca/ge 132-189 is correct.....the others????

    We do have a MC7270 on the sales floor, when my back is ready might need to pull it out of the case and take a look.
     

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  2. c_dk

    c_dk Addicted Member

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    The other channel.......5 more suspects

    And the wrong bias transistor again....hey it's a darlington must be close enough!
     

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  3. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    Hello !

    The one in the first picture is not a usual one but marked with MCINTOSH transistor's part number

    In your second picture :
    The first TR is original motorolla commercial marked MJ15019 (official correspondance)

    the second one (132188 or 132189) is an usual GE/RCA type original transistor marked for MCINTOSH Labs

    The one in your first picture is unknow for me (never seen any before today ! )
    But I don't see any reason to think that it is a counterfeit or a bad one

    If I was you I will change all in once (NPN) and (PNP) and darlington bias TR too !
    Check if the fuse resistor is replaced by an original one or carbon type !

    I will suggest you to change it for a fire proof type , carbon type is not recommended for 100% safety protection :yes:

    Patrice
     
  4. c_dk

    c_dk Addicted Member

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    Have no idea what brand the non RCA 188/189 are.....Mac would never mix brands in the middle of a production run.....planned leftovers always go to service anyway.

    Looks like someone went through the trouble of putting Mac numbers on unknown product, most likely to make it "easy" for a quick repair.

    Unfortunately the left channel overheats and the scope hints at oscillation in both channels.

    Someone obviously cut corners doing a repair at some time in the past.
     
    Last edited: Nov 11, 2013
  5. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    Hello !

    Unfortunately the left channel overheats and the scope hints at oscillation in both channels

    I will suspect that emitor resistor are not original type and may be bad making output oscillations .

    Check if someone put his finger there (on both channels)
    139125 Mc Intosh part number 5LW.15 ohm + - 5%

    T03 drivers need to be original too .

    132203 PNP
    132204 NPN

    Be sure also that both driver PCB are the same part number :yes:
     
  6. Classic_CJ

    Classic_CJ Well-Known Member

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    585
    Certainly very odd about those possibly bogus devices.

    I did note from just checking the manual that there is a serial break-- they show a separate circuit page for the early and the later versions. One change is in the number for the driver transistors. The early series had a selected device, the latter not. Not sure if the latter replaces the former or not, never had to repair an output stage in this model yet.

    c_dk, you're probably already aware of this, but there are two different 0.15 ohm emitter resistors, one inductive (the 139-105) and the other non-inductive (139-125) used in Mac amps that use this emitter resistor value. My 7270 service manual doesn't list the part number of the resistors, but I'd assume it's the 125 as clinic-audio states.

    This leads to something that caused me concern when I last ordered these parts from Mac just a few months ago. I ordered both 105s and 125s, and while they came in separate bags, the resistors inside the bags looked absolutely identical-- no markings that normally appear on the resistor to denote the non-inductive status. (All of which reminds me I never called parts to check with Gail or Brian about this and that I need to before I run out of my old stock and need the new.)
     

     

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  7. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    Classic-CJ

    Oooooh !

    Be carefull and don't open the bags if you don't have confirmation that they are not the same :tears:

    Normally there is differences between the both !

    See my picture

    Where is the inductive and the "non" inductive ?
     

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  8. c_dk

    c_dk Addicted Member

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    Good to see you back CJ.

    I asked him about the WW situation previously. To memory, 2/3s through the mc2205 production run, the WW supplier changed their production process producing non inductive resistors. Mac did not know this until 2205s where showing signs of oscillation. The manufacturer's part number did not change either. The 2nd schematic, 039239, shows the circuit changes applied to deal with this.

    A new part number was created for the non inductive type.

    The ma6200 schematic shows both #s in the parts list but it seems no circuit changes were needed to accommodate the non inductive type.

    New transistors are on the way.....the WW are all non molested rockwoods.
     
  9. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    Where is the inductive and the "non" inductive ?

    nobody find ?

    Non inductive is 139125 the one above (top of the picture)

    The inductive is the one with an L on it after the W ! :banana:
     
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  10. c_dk

    c_dk Addicted Member

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    I do not believe the resistors in the early mc2125 and mc2205 have the "L" in the number. You always need to check the amp against the schematic to insure getting the correct resistors.
     
  11. Classic_CJ

    Classic_CJ Well-Known Member

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    Here's a copy of the document I have that gives the serial breaks for the various models affected by the emitter resistor changes. The original doc is a pretty clunky in wording, so I cleaned it up a bit, but all the data on it is provided. This is what I've always gone by when I've rebuilt output stages on the affected models. Interestingly, this doesn't state anything about inductive or non-inductive, just that the parts are "different".

    I don't know the date this was originally issued, as I inherited it from other techs a few decades back. I do recall the black lines they mention, although that stopped after a few years, and then you had to look for an 'L' or some other marking on the resistor body denoting non-inductive. Here 'tis:

    TWO DIFFERENT .15 OHM 5% 5 WATT RESISTORS

    Parts in question:

    0.15 ohm 5% 5 watt resistor part #139-105

    0.15 ohm 5% 5 watt resistor part #139-125

    Models where parts are used:

    MC2120, MC2125, MC2200, MC2205, MC502, MC6200, MAC4100

    Circuits where parts are used:

    The 0.15 ohm resistors are used in the emitter leg of the output transistors.

    The two resistors have different performance characteristics when used in the actual amplifier circuit. Part # 139-105 SHOULD NOT be substituted for part # 139-125, or vice versa. If the wrong part is installed in the amplifier being serviced, performance and/or reliability will be affected.

    Below the serial numbers shown use # 139-105.
    For the numbers shown and above use # 139-125.

    MC2120 – serial break at AW2857
    MC2125 – serial break at AZ4393
    MC2200 – serial break at AU2735
    MC2205 – serial break at AX8451
    MC502 – use 139-125 for serial CE1001 and above
    MA6200 – serial break at BX1582
    MAC4100 – serial break at BY2340

    We will now mark the 139-105 resistors with a black line on the resistor body to further assist in identifying the correct part.
     

     

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  12. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    Hello Classic_CJ

    I have watched all pictures of all MCINTOSH amp I have repaired during these last 10 years and I found this one (see my picture)

    This is a MC502 driver board and we can see that there is L 0,15 ohm resistors ....(inductive)

    MC502 Service manual say in notes 8 : in unit below CE1947 emitor resistors were 139105 (inductive) but if you read the parts list you will see emitors resistors are part number 139125 non inductive

    All of this make really confusing :scratch2:
     
  13. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    forget the picture !
    sorry
     

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  14. c_dk

    c_dk Addicted Member

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    Moving into new shop space I still have schematics scattered hither, thatcher and yon!

    Have the mc 2125 schematics at hand and while the part number change is noted there seems to be no circuit changes directly realated to the WW change.

    Also no changes noted in the mac4100 service notes.

    Is this just a mc2200/2205 circuit change to accommodate the non inductive type?
     
  15. steelgtr

    steelgtr Well-Known Member

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    My 2105 is in the shop ready to (finally!) be picked up. Problem was a short and transistors were replaced. Is the 2105 included in this "controversy"?

    bob
     
  16. c_dk

    c_dk Addicted Member

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    Hardly a controversy......

    Your mc2105 uses a different design....but needs inductive .56 and .33 WWs.

    We need to get this sorted out.....If techs are taking shortcuts buying questionable origin outputs I doubt they will be tasking themselves to find the correct resistors.
     

     

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  17. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    If techs are taking shortcuts buying questionable origin outputs I doubt they will be tasking themselves to find the correct resistors

    For sure !:thmbsp:
     
  18. steelgtr

    steelgtr Well-Known Member

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    Sorry, maybe should have said confusion. So how do I tell if my repair was done properly? Or doesn't this apply to my 2105 if just the outputs were changed? Sorry, I'm not a tech!

    bob
     
  19. rolltide

    rolltide Super Member

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    Where in the bay area did you take your 2105 for service?
     
  20. steelgtr

    steelgtr Well-Known Member

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    Norm at Sertech
     

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