Kenwood TL 922 help needed

Discussion in 'Amateur Radio Amplifiers' started by WD8BWW, May 22, 2017.

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  1. WR2E

    WR2E Ham Member QRZ Page

    In an earlier post I suggested where I would start.

    That is, the zener bias diode, the metering resistors, and I'm going to add the standby operate relay contacts.

    Take a look at those circuits. When in standby the relay connects the full bias, shorting out the resistor. When in operate the resistor feeds the zener diode and the resistor to ground in the meter ckt. I think that's a 68 ohm?

    Understand the circuit and you'll know what to look at.
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    IIf it didn't blow any fuses, I suspect the plate current meter is reading inaccurately because its shunt resistor has drifted high in value or is open. If it's open (weird) I'd think the meter ccoil would blow up or at least greatly limit the current available for the tube.

    When this happened, what did the grid current meter indicate?
     
  3. WD8BWW

    WD8BWW XML Subscriber QRZ Page

    grid current meter does not move (reads 0) and the plate voltage does not drop. I have been working on other radio repairs and hope to get back to the amp today or tomorrow. I wanted to get thoughts lined up before I started.
     
  4. WD8BWW

    WD8BWW XML Subscriber QRZ Page

    By the way and most importantly. Thanks everyone for your responses and ideas.
     
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    That would have been a great first post for your problem.

    Everyone was guessing for nothing.

    You may get a good answer now. :)

    Good Luck. Happy Holiday.
     
  6. W1QJ

    W1QJ Ham Member QRZ Page

    Most likely the 1 ohm plate meter shunt resistor is open. I'd check that first thing.
     
  7. WD8BWW

    WD8BWW XML Subscriber QRZ Page

    i got some valuable insight and learned a lot about the amp design from these posts, especially on the center tap circuit and coupling. I agree it will help to answer what could be the cause of the tube failure or what the tube failure could have caused. Learning from each other is a great part of this hobby. I will post exactly what I find.
     
  8. WD8BWW

    WD8BWW XML Subscriber QRZ Page

    W1QJ you got it. R6 the reads 1 meg not 1 ohm. Also R7 1.5k 1/2 watt resistor looks like a charcoal briquette. I have the R6 in stock but not the R7 a 1.5k 5% carbon resistor.. just ordered it. I will check all the other resistors on the board.
     
  9. WR2E

    WR2E Ham Member QRZ Page

    What he said.

    That's R6 on the meter board I believe?
     
    Last edited: May 27, 2017
  10. WD8BWW

    WD8BWW XML Subscriber QRZ Page

    yes R6 and R7 are both on the meter board. R7 letting out the smoke likely saved the meter. The remains of of R7 reads 47K.
     

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