Kenwood TL 922 help needed

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

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  1. WD8BWW

    WD8BWW XML Subscriber QRZ Page

    I have a long winded version with details of this post on the repair forum. I thought I would post on this forum in search of a TL922 Guru that might hang out here. Specific questions are can I operate, for the purposes of testing, a 922 with just one tube installed. One of the tubes that came with the amp the filament would not light. The issue is when keying the amp with zero drive the Plate current meter pegs “hard”. I’m reluctant to install the new tubes until I know what is causing this.
     
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    Tubes can do funny things when you try to use them with no heater.

    If the filaments light, Then testing 1 tube at a time can work. But loading control will most likely be off.

    SWR into the amp may be affected too. I would reduce drive greatly while testing.

    Have Fun. Save some smoke for later. ;)
     
    Last edited: May 22, 2017
  3. WD8BWW

    WD8BWW XML Subscriber QRZ Page

    I'm only trying to test with the tube that lights. I just want to get past the plate current pegging.
     
  4. KD0CAC

    KD0CAC Ham Member QRZ Page

    I like to keep in mind with tubes , the 1st thing my tube tester manual tells me to do , check for shorts is the [ 1st ] test , then continue testing ;)
    As for using 1 hole at a time , there may be issues , but I have not heard of damage being done doing this , but checking like you are , there maybe something [ or lots ] I haven't heard yet ;)
     
  5. WR2E

    WR2E Ham Member QRZ Page

    My first exam would center on the metering circuit, switches, resistors, etc.
     
  6. W1QJ

    W1QJ Ham Member QRZ Page

    Be careful, the tube filaments are in series. A small choke balances the small imbalance that might be on the center tap and it would probably be overloaded when using only one tube. I would advise against it and make sure you have two good tubes. The plate meter is probably pinning due to an open plate shunt resistor. You may end up blowing that meter. A word to the wise.
     
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    Operator Error by KA9JLM. To many knobs.
     
    Last edited: May 22, 2017
  8. WR2E

    WR2E Ham Member QRZ Page

    Lou, you think the choke is too small to handle the filament current of one tube?
     
  9. WQ4G

    WQ4G Ham Member QRZ Page

    Are you SURE the filaments are in series? Looks like parallel to me. Each filament is fed off one side of the 'center tapped' filament transformer. It works just like the 240 feeding your house. Each tube is fed with a single leg (side) of the transformer. L3 and L20 are filament chokes and are there to keep RF from getting into the transformer.
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Nope, they're in series, alright.

    The bifilar filament choke that handles all the filament current is L3. L20 is only for cathode bias current to switch between standby and operate bias and is not rated to handle filament power at all -- it will likely burn up. DC cathode current is never higher than 1A peak or 800mA continuous. The filament current of a 3-500Z is 14.6A.

    If you lift L3 altogether (disconnect it), the filaments will still work fine, you'll just lose bias and the tubes will draw heavy idling current.
     
    WA7PRC likes this.

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