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AL-80B taking out finals....

Discussion in 'Amateur Radio Amplifiers' started by AE1P, Jul 3, 2020.

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  1. KP4SX

    KP4SX Premium Subscriber QRZ Page

    That reddish looking color is close enough to brown...and it measured 100 ohms.
     
  2. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Whether it is a 2.0k or a 2.7k, there is no way a set of probes across that resistor should be measuring 100 ohm ohms!

    Nor in receive condition should the RF input connector measure 65 ohms from the center pin to ground.

    Recommendation: Don't try any OTHER experiments on this amp until these items have been traced out fully.

    Pheel


     
  3. W1QJ

    W1QJ Ham Member QRZ Page

    It’s 100 ohm resistor. I’ll repeat. There is a 100pf or maybe 50pf mica cap in series with that 100 ohm resistor and again in series with another mica cap. That network shunts the coil. I have an AL1200 suppressor which has the same set up and I easily read the resistance of the resistor because of the isolation of the caps on both sides. Now, one cap could be open which will totally destroy the suppressor if the amp goes into transmit. You may have to check to see if one of the caps is open to be sure the suppressor is effective.
     
  4. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    It may have the same setup (PCB board configuration) but it does not necessarily have to have the same resistor or capacitance values since the AL-1200 uses a different tube with a different output capacitance.

    According to standard resistor color coding a Red-Black-Red banded resistor with a Gold band at the end is a 2000 ohm (2k) resistor with a 5% Tolerance, and according to Neil's picture, that is what is is.

    https://www.mouser.com/technical-re...MIy8vrv5y56gIVAr7ACh1ptQHEEAAYASAAEgIXefD_BwE


    Pheel
     
    Last edited: Jul 6, 2020
  5. G0JUR

    G0JUR Ham Member QRZ Page

    to my old eyes that resistor looks brown black brown 100 ohms.
     
  6. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Maybe Neal can verify the color banding from the backside pic left to right but it looks Red-Black-Red with a Gold band at the bottom. Even when I printed the pic it looks Red-Black-Red with a Gold band.

    Pheel
     
  7. W1QJ

    W1QJ Ham Member QRZ Page

    My AL1200 has two 100 in parallel and I measure 50 ohms. The colors look like red black red but it’s obviously brown black brown. My resistors and his resistor are the same . He needs to check for any open mics on either side or both.
     
  8. AE1P

    AE1P XML Subscriber QRZ Page

    He needs to check for any open mics on either side or both.

    Will do.
    Hard to tell with cell-phone pics...but resistor is Brown-Black-Brown...
    Thanks to all for input & help...I'll post results...
    73,
    Neil
     
  9. AE1P

    AE1P XML Subscriber QRZ Page

    There is a 100pf or maybe 50pf mica cap
    Looks to be 100 AL-80B1.jpg
     
  10. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    So the pics rendered the Brown bands as Red but your eyeball inspection says the Red-colored bands are actually Brown bands? Amazing!

    My Kyocera cell phone camera has never rendered a Brown resistor band as Red.

    None of this makes sense but measuring the mica caps might tell us something. Look at the values marked on the caps and please let us know what they actually measure with at least one lead out-of-circuit.


    Pheel
     
    Last edited: Jul 6, 2020

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