McIntosh - Hints and Kinks

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

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  1. brichter

    brichter Well-Known Member

    Messages:
    727
    Location:
    SF Bay Area
  2. vyik

    vyik New Member

    Messages:
    3
    Hi again. Finally had some time to work on my mc60. I was able to change out all the caps but left c12 and c13 alone since the previous owner changed it out. Instead of .25uf he used .22uf. Should i change this back to .25uf?
    [​IMG]

    When i got to the back i notice resistor r18 and r19 was also changed. its a huge resistor and im not sure what is the propose for this as my other mc60 didnt have this huge resistor. should i change it out?

    [​IMG]

    I also changed selenium rectifier to 1N4007 and bias capacitor to a 22uf and in the process of changing the diode resistor to 9.1K 1/2W resistor.
     
    Last edited: Feb 15, 2013
  3. dewickt

    dewickt Will fix about Anything

    Messages:
    3,377
    Location:
    Knoxville, TN
    .22 uF is OK
     
  4. Rich Andrews

    Rich Andrews Well-Known Member

    Messages:
    921
    Location:
    TX
    MCD7008 blue filter removal

    Trying to remove the blue filter that is glued to the back of the glass so that it can be cleaned or replaced? Dental floss works good and is safe and easy. Simply pull the dental floss between the filter and the double sided tape. Having a helper hold the glass still is almost a must.
     
    Last edited: Mar 3, 2013
  5. Rich Andrews

    Rich Andrews Well-Known Member

    Messages:
    921
    Location:
    TX
    MCD7008 blue filter removal

    I forgot to mention that if done right, simply pressing the blue filter back in place is all that is needed. That double sided tape is still plenty sticky.
     
  6. dewickt

    dewickt Will fix about Anything

    Messages:
    3,377
    Location:
    Knoxville, TN
    MR73 low sensitivity

    Have a MR73 on the bench that was showing 12 uV sensitivity, not good!!
    Looking at the stage gains I zeroed in on the first RF amplifier Q1 an N channel J FET. Checked the parts collection and found MPF102 just right as a drop in, the end result after a quick alignment is less than 1 uV for 3% THD, beats specification, just what the doctor ordered.
     
  7. priceb

    priceb audio/ocd

    Messages:
    99
    Location:
    Gate City, Va.
    Terry, Your help

    Terry, been ~ 3 yrs. since I was at your shop. You were such a great help to me (who know's nothing) You done my MC-2100, a Big Pioneer Amp. and benched my My MA-5100, also bought a 110-Z from you guys. You taught me how to clean the outputs on my amps. Why not share this info. w/other guys? It works great. Just polished outputs on a KENWOOD KA-9100 and they look beautiful. (just a 3/8" rubber hose)

    Also, how about the WOODY we looked at?

    Thanks,
    M.C. Price
    Gate City, Va.
     
  8. johndoe1

    johndoe1 Member

    Messages:
    59
    MA5100 Bass Tone control ground hum at midpoint

    Dear experts,

    I am doing problem determination on a MA5100 with a serial # of 79H69.

    Everything is in great working order however with very efficient speakers, Altec 416/806 on 811 horns the Bass control when you grab the back ring, the RIGHT give a mean humm and static at about the 1 oclock position., if you grab it and turn from the inner ring the knob turns no problem. The pots are clear and clean on both Treble and Bass however the HUMM - like a open ground loop or a interconnect not connected is a problem at the 1 oclock position; could it be a bad POT and a drop out. Happens with a source or without and volume of course increases the noise...scratchy and humms like a ground loop...

    Taking off the knobs if you use 2 fingers on the back clutch ring of the dual POT you get HUMM and scratch at about 11o'clock to 1 oclock.

    ANy ideas on the next step to problem determine?

    Thanks
     
  9. johndoe1

    johndoe1 Member

    Messages:
    59
    Ma1500 bass control problem pt 2

    Ok tonight i turned the pot with a heavy silicon rubber pot handle holder...no noise or ground sound when it's turned by hand. I did notice if i hold the back right ring a lightly wiggle it - ground noise. Maybe the center lead it touching something at ground? I was unable to find the schematicf or the reamp bass control section. Any ideas? Terry?
    C
    Thanks john
    P
    When i checked the conne tions i nside looks normal although i have yet to probe on a scope
     
    Last edited: Mar 20, 2013
  10. dewickt

    dewickt Will fix about Anything

    Messages:
    3,377
    Location:
    Knoxville, TN
    Shaft is dirty and not getting a good ground, soak some DeOxit down the shaft, remember D5 for the shaft and F5 for the control its self.
     
  11. johndoe1

    johndoe1 Member

    Messages:
    59
    RE: MA5100 and lubricant type

    terry,

    first thanks for the guidance. Second I assume the best way to do this is invert the unit to it sits with the shafts facing skyward and D5 down into into the shaft. As for lubricant in the control is Silicon lubricant for electronics a better way to go. I assume NO lubricant for the shaft after D5. I normally use MCL.

    Thanks,
     
  12. johndoe1

    johndoe1 Member

    Messages:
    59
    MA5100 bass tone contrl problem

    Terry.

    I cleaned and lubed same issue. When i have my hand on the metal rack this sits on and move the controlol no issues.

    anything else i can do?

    Thanks john
    Maybe i am not getting anything or enough in the back pot control...the base? V. The shaft from the front
     
  13. gdillingham

    gdillingham New Member

    Messages:
    16
    Location:
    Cincinnati
    Lethargic MC240 power on

    Just recently my MC240 has begun not powering up immediately when I apply AC to it. Turn on the power and it sits for maybe 3-5 minutes than all of a sudden begins to work. Looking at the schematic nothing jumps out a me that suggests it could be the culprit. Any suggestions?
     
  14. dewickt

    dewickt Will fix about Anything

    Messages:
    3,377
    Location:
    Knoxville, TN
    First question, do the tubes light up during the delay ? if yes you probably have a bad power supply capacitor (doubler cap), if no it may be the NTC startup resistor.
     
  15. gdillingham

    gdillingham New Member

    Messages:
    16
    Location:
    Cincinnati
    An Aha! moment. So THAT's what R56 is for. Learn something new everyday. No, the unit is totally dead for several minutes until the tubes light up. Thanks, Terry. Where canI source something like this?
     
  16. dewickt

    dewickt Will fix about Anything

    Messages:
    3,377
    Location:
    Knoxville, TN
    CL-50 NTC, thermal resistor available from most supply houses, or from the factory parts department 800-538-6576.
    The MC240 uses a voltage doubler type power supply, the NTC is there to limit the turn on surge to the supply, makes the power transformers surge less, and doubler capacitors last longer.
     
  17. lmwhite111

    lmwhite111 Member

    Messages:
    59
    Location:
    Texas
    Please educate my ignorance. With all these problems with McIntosh equipment why is it so a) popular and b) expensive?
     
  18. dewickt

    dewickt Will fix about Anything

    Messages:
    3,377
    Location:
    Knoxville, TN
    Most units we are collecting and using daily are up to 50 years old and still sound as good and look better than ones by other manufacturers that are 10 to 20 years old. Simply put they are worth putting time and money in to keep operational and working to specifications that most newer brands can only wish for.
     
  19. brichter

    brichter Well-Known Member

    Messages:
    727
    Location:
    SF Bay Area
    You realize we're discussing a lot of equipment that is easily 30-40 years old, right? :yes:

    The longevity and performance of these products are the reason why they're popular, and with popularity comes cost. :music:
     
  20. Rodeodave

    Rodeodave hates ground loops

    Messages:
    282
    Location:
    in the Alps
    Just to give you some examples of recently discussed models:

    MC60: Weight 46 lb. Sold from 1955-1961. Last retail price $219.00
    MC240: Weight 56 lb. Sold from 1960-1969. Last retail price $288.00
    MCD7008: Weight 24.5 lb. Sold from 1992-1996. Last retail price $2200.00
    MR73: Weight 24 lb. Sold from 1969-1971. Last retail price $549.00
    MA5100: Weight 25 lbs. Sold from 1966-1972. Last retail price $449.00

    All of the above can usually be easily fixed by replacing dried up electrolytic caps, replacing the occasional out-of-spec resistor and fitting a new NTC thermistor. The build quality of these units is outstanding, as are measured and percepted performance.
    And if you some research and adjust for inflation, you'll usually see that the used prices are above or equal to the original retail price, which makes them a reasonable investment.
     
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