SB-221 Heathkit AMP Bias Mod T/R Relay 100k Question

Discussion in 'Amateur Radio Amplifiers' started by N0OHL, Dec 4, 2019.

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  1. N0OHL

    N0OHL Ham Member QRZ Page

    I have been going thru a working SB-221 and am getting ready to what is called the Bias Mod. I would like to thank W1QJ for his great description of the Mod details.

    However, checking the details of how my SB221 was built, I found something interesting. The resister to be moved to the next contact in my AMP is 54ohms -- and everything I can find says it should be 100k. However, the relay/amp seems to be working all right.

    However, I am thinking I should replace th 54ohm Resister with a 100k one when I move the wires around with W1QJ directions.
    Pictures below of how it looks now ( before Mod ) ( the extra white wire is to power a Soft-Key -and will be left)
  2. N0OHL

    N0OHL Ham Member QRZ Page

  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    You're reading the color code from the wrong end of the resistor.

    That's 100K: Top stripe brown (1), next black (0), next yellow (4 zeros) = 100,000. The green band is the tolerance: Green = 5%.
    K7TRF likes this.
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Yup, that's a 100k resistor...
  5. N0OHL

    N0OHL Ham Member QRZ Page

    Wow....sure glad I put a picture here
  6. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Well, there's no harm in replacing the 100k resistor with a.... 100k resistor other than the cost of that resistor :)
  7. AI3V

    AI3V Ham Member QRZ Page

    Fixed it for you :D

    KS4W likes this.
  8. W2VW

    W2VW XML Subscriber QRZ Page

    I like the last picture. It looks like the components are covered with fuzz from a capacitor explosion.
    KD2ACO likes this.

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