HRO-60 - Question About R67

Discussion in '"Boat Anchor" & Classic Equipment' started by KW4H, Jun 30, 2021.

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  1. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    I'm in the midst of restoring an HRO-60 (ER 345) that's pretty beat up, and has been monkeyed with over the decades. The restoration is mostly coming along fine, and so far a number of defective, incorrect, or incorrectly installed parts have been replaced. Recently, when working around V12, I found a 22K resistor masquerading as R67. According to the diagram and the parts list, this should be a 220K. Strangely, however, the resistor appears to be factory because the soldering work on its leads appears to be original. Does anyone here have any idea why that resistor should actually be a 22K and not a 220K, based on the schematic? I'm prepared to switch it to a 220K but am looking for advice.

    Thanks, Steve - KW4H

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  2. W1NB

    W1NB XML Subscriber QRZ Page

    Attached Files:

    Last edited: Jul 1, 2021
  3. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

  4. SM0AOM

    SM0AOM Ham Member QRZ Page

    Both values may be correct.

    In the earliest production runs of the HRO-60, the value was 22 k, the same as in the HRO-50T1, but later it was changed to 220 k.

    I have not been able to detect any difference.

  5. KI4ZNV

    KI4ZNV Ham Member QRZ Page

    It's carrying an audio signal into a point with about 200K impedance, as set by R33 and R34. So if it's a 220K resistor, it will drop the audio level about 6dB compared with 22K. Frequency response won't change very much.

    I see no reason not to use either value but I can see why they'd make a factory change to a lower value. I don't see why they'd raise the value unless they're worried about keeping the audio level down a bit at that stage.
    WA1GXC likes this.

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