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McIntosh - Hints and Kinks

Discussion in 'McIntosh Audio' started by dewickt, Jul 1, 2004.

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  1. RShackleford

    RShackleford Active Member

    Messages:
    257
    Maybe you don't know, but tantalums are a type of electrolytic. And yes, I'v also heard they tend to fail.
     

     

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  2. pcrosewood

    pcrosewood Active Member

    Messages:
    161
    Location:
    Halifax, Nova Scotia
    Replace the tantalums with aluminum caps?
     
    Last edited: Dec 3, 2013
  3. RWright

    RWright New Member

    Messages:
    14
    More info on MC40s

    Hello,
    I also have a pair of MC40s that I recapped years ago. I also changed out the selenium rectifier on the bias power supply. However, I never added any resistor in series with the rectifier diode as you mention. I used a variac and adjusted the pin 3 of the 6L6 t 470v. Now I get -168 and -58 volts on the bias lines. Should I put a pot in series with the transformer/diode to trim this, and then replace with fixed value? It seems like it would be alot higher than 470-ohms, but I calculated on the dc side.

    Since I originally posted this, (without replies) I have tried to adjust the bias by setting the 6L6 voltage to 470v, then using a pot in series with the AC side of the bias voltage I adjusted for -52 volts on the bias. However, when I do this the 6L6 voltage drops to 460v. Is there another issue with the amp I might be overlooking? Thanks.
     
    Last edited: Dec 5, 2013
  4. pcrosewood

    pcrosewood Active Member

    Messages:
    161
    Location:
    Halifax, Nova Scotia
    I replaced all the electrolytic caps in my MX 114 as per Terry's suggestions, with Nichicon KZ caps and wow. The MX 114 went from being dull and lifeless to being dynamic, detailed, rich highs with solid bass, smooth with rich warm resonant mids...I'm trying to describe what you can only appreciate by listening. People have suggested to me not to put money and effort into this preamp. "They weren't all that great to begin with" I was told. Well, I beg to differ and this preamp with my Mac 2105 is providing me with listening bliss...it's all I'll ever need or want. Many thanks to Terry and all on this site for being so open and generous with your experienc and knowledge. Can you tell I'm happy with the resuits :)
     
    zenith2134 likes this.
  5. Mike Gibson

    Mike Gibson Modulator Staff Member Super Mod Subscriber

    Messages:
    9,029
    Location:
    Dufur Oregon
    Please use this to add helpful hints you have discovered so that others can benefit from your knowledge.

    Please ask questions such as what caps to use or how do I in the main forum or PM the techs who frequent this forum.. That way this thread will only contain actual helpful hints. The other thread is full of questions about caps, procedures etc. All posts unrelated to actual hints will be deleted so as to keep this thread relevant. Thank you for your cooperation.


    Mike
     
  6. RShackleford

    RShackleford Active Member

    Messages:
    257
    At least one of the older tube amps was released with minor variations of the circuit. For mine, the MC40, the older version of the circuit is the one seen in virtually every schematic found online. I only know about the newer circuit because it's in the printed manual that I have; it has dotted lines and notes referencing the older one.

    The reason it's helpful to know about the newer circuit is that it has fewer components - two fewer capacitors on the main circuit board, and more significantly, one fewer resistor and one fewer capacitor in the power supply. This last item means that it's more feasible to replace the expensive, bulky, and difficult to source multi-section FP-mount can capacitor with a single-section cap (with high enough voltage rating). The power supply just ends up having 4 caps: the two in the voltage doubler, a big one for B+, and one much smaller (so an axial lead part can be used). I am mod'ing my older one to use the newer circuit while I rebuild the pair.

    Presumably the newer circuit is at least marginally superior as well - I doubt the changes were made just to save a few cents on parts (the newer version is still manufactured with the multi-section can).

    The attached snippet from the schematic shows the relevant section; bear in mind that the values of two resistors on the circuit board (R11 and R12) are also different between the two versions (as well as some capacitors not related to the PS).

    NOTE: I just edited to show the complete newer version of the schematic.
     

    Attached Files:

    Last edited: Sep 28, 2015

     

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  7. Scifi

    Scifi Super Member

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    1,229
  8. Scifi

    Scifi Super Member

    Messages:
    1,229
    You can monitor the current when turning on electrical equipment to make sure it isn't drawing too much current. A common cause of this problem is leaky filter capacitors. I use a Micronta model 22-161 clip-on type ammeter with a receptacle-plug adapter (see pictures). I also recently got some test sockets (one octal and two nine pin miniature) so I can test voltages without drilling extra holes and adding test sockets to the device and/or opening the device to test it.


    http://support.radioshack.com/support_meters/doc21/21584.htm

    http://support.radioshack.com/support_meters/doc39/39829.htm
     

    Attached Files:

    Last edited by a moderator: Jan 5, 2014
  9. rbnjr2

    rbnjr2 New Member

    Messages:
    34
    Location:
    MUKILTEO
    mc40

    I would like to try a pair of mc30 or mc40 monoblocks to power just the tweeter
    of my proac response D18 speakers. the manf suggests a tube to power them and i am very very curious how they would sound being tube powered. by what you have shared it appears you have a very good amount of knowledge in the tube design of power amps. mcintosh has always built their products with a lot of pride inside and out with quality number one. thank you for sharing and i look forward to owning one of the mc30 or 40 monoblocks.

    thank you.
     
  10. ADiG

    ADiG New Member

    Messages:
    3
    hi, someone can tell me how many millivolts is the bias voltage of the power section amplifier MA7000?
    in my Mc MA7000 the values ​​are different and left heatsink up more heat.
    you could read the schematic diagram at the "heat sink" page, but is not available online
    Many thanks
     
    Last edited: Aug 5, 2014
  11. ADiG

    ADiG New Member

    Messages:
    3
    there is a technical MC in this forum, who knows the value in mv. be set?
    Around the forums, I've read several posts with the same problem (the left channel of the ma7000 warming). Perhaps there was an error setting this value in the assembly ...
    by my measure, it is not very clear about the difference measured between the two channels:
    left 10.00 mv. - Right 5.7 mv.
    I brought the left channel to 6.00 millivolts and does not heat up more, but knowing the exact value, I would stay in peace!
    Thanks to those who helped me
     

     

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  12. ADiG

    ADiG New Member

    Messages:
    3
    I warmly thank Ron C. and Mr. Landon from Mcintosh Lab for the support lent me - thank you!
     
    KentTeffeteller likes this.
  13. pcrosewood

    pcrosewood Active Member

    Messages:
    161
    Location:
    Halifax, Nova Scotia
    Mc 2105

    Is there anything specific I can do to tighten up the bass on my 2105. Are there specific caps,resistors, transistors that could be replaced ? Any and all suggestions would be helpful and I'm really hoping Terry DeWick chimes in.
     
    Last edited: Sep 3, 2014
  14. dewickt

    dewickt Will fix about Anything

    Messages:
    3,396
    Location:
    Knoxville, TN
    Caps on the input preamp, and main filters, the main filters do the most.
     
    LPplayer likes this.
  15. pcrosewood

    pcrosewood Active Member

    Messages:
    161
    Location:
    Halifax, Nova Scotia
    Thank you Terry.
     
    Last edited: Sep 6, 2014
  16. rpoli2518

    rpoli2518 New Member

    Messages:
    17
    Location:
    Canada, Toronto
    Hi fellows,
    I have McIntosh mc2200 amp and McIntosh c33 preamp. Right channel is louder then Left. Tried to switch rca output from main on preamp right to left and left to right. The problem switched also. So its preamp, not amp. What section do you think I need to check. The sound is clear but unbalanced. It has amplifier monitor board. Do I need to check it first and what parts?
    Have multimeter only.
    Thanks in advance
     

     

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  17. duder1982

    duder1982 Active Member

    Messages:
    244
    Location:
    The east coast of Nebraska
    Good thread.
     
  18. RadioTech64

    RadioTech64 New Member

    Messages:
    1
    MC2105 Bias Problems?

    Hello everyone. A newbie to the forum here that has read and taken in a wealth of good info already :) Retired 2 way tech who does audio on the side..With that being said I have a head scratcher 2105 on the bench. First of all according to the customer it would randomly blow line fuses,then from what he explained shut down to thermal overload..this is where I enter :) Powered up and found right channel heatsink heating to 85-90° quickly. Checking the output transistors (132-036 and 132-070) found no leakage but gains all across the board. All were replaced with MJ15003 ON/Motorola parts.Good output and no distortion but right heat sink heats over period of an hour to 80° with no signal applied (idle). Sounds like bias issue to me so the driver boards are swapped and only a slight change.BTW Main caps were replaced due to leakage. From what I gather the bias diode is under the driver transistor on the driver board. That checks OK (compared to other side board) but does read more like a dual diode in series. Question here is: is there a good place to measure the bias current ( across the emitter resistors?) without having to install jumpers?

    Also my bias resistors are 27 ohm each side and have aged to 28 and 29 but..I understood normally they are 22 ohm. Is there a specific target current for biasing these amps? BTW there is roughly a DC Offset of .22 on left and .13 on right at idle,but this is an autoformer design so that shouldn't be a major player.

    Sorry for a long winded first post but I want to tell the whole string of events as I know it.

    Any tips,suggestions,or help greatly appreciated!

    Regards,

    Wayne
     
  19. Josar54

    Josar54 New Member

    Messages:
    4
    Dear Audiokarma friends, I'm fixing a Mcintosh MC 2300 and am having problems with the design digram of the top cap, could someone give me a scale design or a good photo to make it print to the top.

    Best regards
    Jose Armando
     
  20. So...MAC4100 here

    Only hums ( unchanging 60hz hum) when something is plugged into one of the inputs

    Plugging an opened ended RCA cable into the Recorder Tape Outs makes the FM audio level jump way up and then FM starts playing competing stations

    What the heck?

    I work on receivers all the time and do NOT see this anywhere else
     
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