Dentron GLA-1000B... a few things I need help with

Discussion in 'Amateur Radio Amplifiers' started by KC5DFP, Sep 26, 2019.

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  1. W1QJ

    W1QJ Ham Member QRZ Page

    The 10 meter toroid would be the same color as the 15 meter toroid only with less turns on it. The caps should be slightly lower on each side than the 15 meter caps. BTW....How does the swr look on 15?
     
  2. KC5DFP

    KC5DFP Ham Member QRZ Page

    Hi Louis.

    The SWR on 15 is flat, so no issues there, or on any of the lower bands.

    The 10M toroid in the amp when I got it was red and the caps were 5uf and 12uf, and 15m caps are 5 and 150 uf, so probably close....
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If they're really uF, I'd think they'd resonate down in the 100 Hz region.

    You must mean uuF or pF.:p

    Why not use an analyzer, terminating the board in a 100 Ohm resistor or something, and see where the circuit resonates (read and record R+/-jX)?
     
    WA7PRC likes this.
  4. KC5DFP

    KC5DFP Ham Member QRZ Page

    You’re right, I meant pf.
     
  5. KC5DFP

    KC5DFP Ham Member QRZ Page

    Is the a quad of 6LQ6s look like 100 ohms? If so I can unsolder the coax cable from the board, add the resistor, and take the measurement.
     
  6. W1QJ

    W1QJ Ham Member QRZ Page

    Did you try scanning the whole 10 meter band checking for a low swr someplace?
     
  7. KC5DFP

    KC5DFP Ham Member QRZ Page

    Yes I did. Unfortunately the SWR was off the scale no matter what frequency.
     
  8. W1QJ

    W1QJ Ham Member QRZ Page

    If an input is anywhere near being in the ball park the am will show some amplification and a high swr but it sounds like your signal is being grounded. Maybe there is a jumper to ground on the backside of the board that needs to be removed a la Aneritron?
     
  9. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Yeah, you could do that. Do you have an antenna analyzer?
    You've got to find where that input circuit is tuned to know which way to go with the coil and caps, or determine that there's something open or shorted as Lou W1QJ suggested.

    Unit's unplugged and open.
    Sub a 100 ohm resistor for the cathodes (pull the tubes and put the R from pin 3 to ground).
    If the relay is an open frame, put a Q-Tip or toothpick in there to close the input circuit (be gentle).
    If not, jump K1A contacts or feed the analyzer into point "C".
    Set the bandswitch to 15m and do a sweep to see how it's supposed to look when it's working.
    Set the bandswitch to 10m, do a sweep, and see what happens. Go outside the band for clues.

    Edit~~~~

    Hi Lou, does he need relay power to switch the input circuits?

    If so, you can pull the tubes, install the 100 ohm resistor.
    Secure the anode leads so that there is no possibility of them touching anything (a touch of black tape and a zip tie or two).

    Close up the box and put the screws in.

    Run the analyzer into the amp and perform the tests powered up.

    Be very careful every step of the way doing stuff like this.
     
    Last edited: Oct 12, 2019
  10. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    OK, Please don't take my suggestion of running the amp for this test. I didn't think about the bias relay switching into that resistor!

    Missed finishing my edits...

    If there are relays that need power to do this test, we'll come up with a different way!
     

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