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Need Substitutes For BF871 and BF872 Transistors - Traynor BLOC 100K amp

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  • #16
    A quick check of op amp voltages may turn up something also and save you from unsoldering all of them. Generally speaking, if you have DC on pins other than the supply pins, there is something wrong with the op amp. That is a generalization and not always true, but it's a good place to start looking.
    "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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    • #17
      Originally posted by nevetslab View Post
      Since the collector voltage of Q19 has pulled loads of current thru the 220 ohm collector resistor, while the zeners shows they're ok, it suggests you have a high current drain on where the supply connects to off '+15A' . It seems to rule out connections to '+15B' or that would be dragged down.
      There have been a few conflicting readings, but it seems there is a large voltage drop between +15A and +15B. (post #10 and #12)
      This would imply that it is the +15B supply being loaded down.
      Still waiting for measurements and + and - 15B supplies requested by Dave H in post #14.
      Originally posted by Enzo
      I have a sign in my shop that says, "Never think up reasons not to check something."


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      • #18
        Ah...I missed that.......thanks!
        Logic is an organized way of going wrong with confidence

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        • #19
          Hey guys, I have some other matters to attend to. I'll get back on this Traynor next week. Thanks

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          • #20
            I finally fixed this monster. I found a bad 2N5401. I had some on hand, so I changed them all out. It's been running for 2 hours, and no overheating. +15 and -15 voltages are good. All functions working. Sounding great. I have to also mention how bad the Philips brand electroytics were in this amp. All were around 50% out of tolerance, or worse. Anyway, Many Thanks to you all for your time and guidance. I truly appreciate you.
            Coop

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