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Problems with Heathkit IG-18 (Modified) rebuild.

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  • #16
    Originally posted by Enzo View Post
    I only see the pics in post #2, and the empty small xstr spots look to me to have the B in the center. Are they TO92 or are they round ones?
    That one is part of the Schmidt trigger and was originally a small round metal case. The others in the sine wave portion were originally TO-98, which the 2N3417s are. The PNP substitutes im using, 2N3906s are TO-92
    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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    • #17
      I don't know. I think of the man hours I've already put into this thing. I wonder if I should have just rebuilt it to use the HP-339a circuit. I got a VCR2N jfet for the AGC just for this purpose.




      But I hate to give up on it now.
      I'd like to eliminate the switches as the problem. Can you guys suggest something I could put in place of the notch filter just to see if it oscillates or biases?
      If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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      • #18
        Sorry, no suggestions for the notch filter.
        But Q5 base is measuring pretty much a double diode drop from B+ ?
        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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        • #19
          Problem Solved!

          Just bought an IG-5218 in mint condition for $52 off ebay.

          The 5218 seems to be pretty much the same circuit as the IG-18. But the one I bought seems to use better parts and hardware.

          Click image for larger version

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          Works great. Modified the power supply board to use a LM317 regulator, and removed the neon and installed an LED.
          If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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          • #20
            Will you be able to use it to figure out what's wrong with the other one?
            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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