The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

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  • Tektronix AM503: Recapping

    It turns out that the Tektronix AM503 with the 4 MHz oscillation (B075593) had a 2 MHz oscillation after I replaced C165:

    Tek AM503 - corroded capacitor
    Tek AM503 – corroded capacitor

    So, despite it not showing any leakage or damage, I replaced C155:

    Tek AM503 B075593 - C155
    Tek AM503 B075593 – C155

    Which had stopped being a capacitor some time ago:

    Tek AM503 B075593 - C155 measurement
    Tek AM503 B075593 – C155 measurement

    I also replaced C165 with a newer capacitor.

    Again, having the hood up, I pulled C452 and C462 from the ±19.3 V supplies:

    Tek AM503 B075593 - C452 C462
    Tek AM503 B075593 – C452 C462

    Despite the 1987 date code, they seemed to be in fine shape, but I replaced them anyway. The new caps have a 50 V rating, not the original 63 V: only a factor of two headroom.

    The four new capacitors in their new home:

    Tek AM503 B075593 - replaced caps
    Tek AM503 B075593 – replaced caps

    The power supply voltages looked clean before and look clean now.

    The AM503 still has the mysterious 4 MHz oscillation, so the capacitors weren’t the problem. Even though the amp is still sick, I feel better.