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Heathkit TA-17 Amplifier

Discussion in 'Troubleshooting and Repair' started by Ron Cianciaruso, Apr 14, 2016.

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  1. Bart Rydzynski

    Bart Rydzynski

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    Apr 14, 2016
    You have a good opportunity to learn from this problem. You theorize what the problem is and it's solution. Pull Q6 and see if the results match your theory. Yes? Great! No? Why not?
     
  2. Ron Cianciaruso

    Ron Cianciaruso

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    Apr 14, 2016
    I now understand a little more here. The X29a829's I bought to replace the originals indeed did have different layout of the pins... They were EBC.... so I removed them all and replaced them with the originals.

    The 2N3391, 2N3859A and the 2N3393 seem to be the same package.

    With all the correct parts in now, the guitar still has low volume and distortion in the guitar jack.
    In the Mic jack I've adjusted things to your suggestion and it seems slightly distorted
    The Bass Jack is not working at the moment, and i see I still only have 8-10volts C103.

    I am thinking that since I have had such wild voltages flying around this thing, the best bet is to get all new transistors ( The right ones) and see where I land. I think I am close here....

    Make sense ?
     
  3. Ron Cianciaruso

    Ron Cianciaruso

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    Apr 14, 2016
    Pulling Q6 had no bearing.. see my last post :)
     
  4. Bart Rydzynski

    Bart Rydzynski

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    Apr 14, 2016
    Replacing all the transistors may be your best bet since you do not have a transistor tester and cannot verify their performance. If you continue and enjoy working on transistor circuits, you may want to look into a transistor tester for your work bench. It will pay for itself in aggravation saved the first time you use it.
     
  5. Ron Cianciaruso

    Ron Cianciaruso

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    Apr 14, 2016

    Very good advice on the tester. I am going to order the transistors now and will report back when they arrive and I get them installed. You've taught me a great deal so far I am sincerely appreciative of your time. Have a wonderful week Bart.... and thank you !

    Regards
    Ron
     
  6. Bart Rydzynski

    Bart Rydzynski

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    Apr 14, 2016
    My pleasure. I really enjoy helping you because you have an eagerness to learn. Will be waiting for your next update. You too have wonderful week!
    Regards,
    Bart
     
  7. Ron Cianciaruso

    Ron Cianciaruso

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    Apr 14, 2016

    Parts are ordered and I also ordered one of these DCA Pro testers... Good stuff.. this will help me tremendously as I do more work with transistors ( Which I love)... thanks

     
  8. Bart Rydzynski

    Bart Rydzynski

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    Apr 14, 2016
    Good choice. I've heard good things about this tester.
     
  9. Ron Cianciaruso

    Ron Cianciaruso

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    Apr 14, 2016
    Bart - A question.
    In my quest to find the correct X29a829 I came across a BC640TA which appears to have exactly the same properties as the X29A829 ( PNP 80V 1A to TO-92) and on the data sheet the PINS are correct for this package. I tried using NTE159 but they have the wrong pins as described yesterday.

    Some Heathkit sites say to use the 2N3806

    Since I am a transistor newbie... is the BC640TA ok in your opinion ( I did check the data sheet and it looks right to me). Thank you again
     
  10. Bart Rydzynski

    Bart Rydzynski

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    Apr 14, 2016
    ???.... couldn't find any data on the BC640TA or X29A829. The 2N3806 has a max collector current of 50 mA, and the NTE159 has a max collector current of 800mA. The NTE159 is more robust in this respect. I've used NTE devices for years and swear by them and would be my first choice. A 2N3906 would be my second pick. Rearranging the leads on the NTE159 to fit the board is no problem.
     
  11. Ron Cianciaruso

    Ron Cianciaruso

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    Apr 14, 2016
  12. Bart Rydzynski

    Bart Rydzynski

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    Apr 14, 2016
    OMG! Mouser is my number one source for parts but I didn't check with them. Go figure. Thanks for the link. The BC640TA looks to be a good sub and is certainly worth consideration. A quick note on transistor subs: Generally, you can make an educated choice on a sub by reading the data sheets. Oscillator circuits and RF amps can be extremely touchy and require an exact replacement. I once had a shorted RF transistor that I replaced with a NTE replacement. The amp still did not work. I spent several hours working on the thing before I finally consulted NTE's data sheet. It clearly stated "This device may not work in all circuits". I installed an exact replacement transistor and the amp worked as intended. The embarrassing part was a co-worker warned me NOT to use the NTE part. Lesson learned.
     
  13. Ron Cianciaruso

    Ron Cianciaruso

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    Apr 14, 2016
    Good evening Bart. I have a mystery on my hands. I received all the new transistors, tested them, checked the config and installed them all. Guitar Channel words but distorted. Mic channel works and I can control the distortion in the way you described earlier. The Bass channel has nothing. I checked C103 and have 60v on the + side when it should be 24. Checking Q4, Q5 and Q6 I do not have the correct voltages.... now the mystery.

    While checking around I see R110 on the schematic listed as 10K. Printed on the circuit board it says 100K. I have previously replaced the resistor with a 100K and am wondering if there was a field bulletin on R110 being printed incorrectly and I need to put in a 10K instead. I am hesitant to change it now as I do not want to start blowing out transistors again.

    Would you know from experience if sounds off. 100k does seem kind of high in that circuit config, but I defer to your expertise. :) Thank you sir..
    Ron
     
  14. Ron Cianciaruso

    Ron Cianciaruso

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    Apr 14, 2016

    Clearly the install pages show R110 as 10K, so I have changed it... however no change. My sleuthing skills will continue to dig until I find the culprit - Thanks
     
  15. Bart Rydzynski

    Bart Rydzynski

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    Apr 14, 2016
    Hi Ron,
    My schematic shows R110 as 100K. Assembly picture also shows R110 as 100K. I have a production run change order dated November 19, 1968 and no change (at this time) was made to R110. Is the part number on the circuit board 85-188-1 or 85-188-2?

    60 volts on C103+ indicates Q6 is not conducting. Q6-B should be very close to 600 mV. What are the voltages on Q4-BCE, Q5-BCE, Q6-BCE?
     
  16. Ron Cianciaruso

    Ron Cianciaruso

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    Apr 14, 2016
  17. Ron Cianciaruso

    Ron Cianciaruso

    54
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    Apr 14, 2016
  18. Bart Rydzynski

    Bart Rydzynski

    39
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    Apr 14, 2016
    C103+ has 60 volts and Q6-C has .46 volts? Check the resistance from the + lead of C103 to the lead of Q6-C. It should be less than one ohm.
     
  19. Ron Cianciaruso

    Ron Cianciaruso

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    Apr 14, 2016

    Good News.. I've solved the voltage issues... The Q6E circuit trace was lifted ( from too much soldering I fear) and there was no connection. I have fixed the pad and reinstalled the transistor and have proper voltage now.
    I still have the 10K resistor in there - do you think I should go back to 100K before I cause other damage ? The board does say 100K but my book says otherwise.

    Thanks for your help on this voltage issue, but glad I was able to find it and fix it ( with your encouragement ) .
    I need to start thinking about the LDR as well and what I will use.. at any rate, allow me to test this thing out and check voltages throughout and I will let you know what else I find.

    Thanks again Bart - be back to you.
    Ron
     
  20. Bart Rydzynski

    Bart Rydzynski

    39
    0
    Apr 14, 2016
    Did your manual come with your amp? If you bought the manual separately, it may be for a different production run and that could account for the difference of R110. R110 and C102 are for frequency compensation so you can ignore them for now.
     
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