Viking Valiant modulator current 250 ma

Discussion in '"Boat Anchor" & Classic Equipment' started by K1OIK, May 23, 2020.

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  1. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    The video may not be that helpful


    Here are the facts.
    6146 were swapped out with no change, noted 22 ohm resistor in the plate cap was cracked, likely a result of the over current.
    If I remove either 6146 current drops by about half, if I remove them both very little current.
    bias voltage on 6146 -35v, adjustable -37 to zero.
    Output of bias rectifier -175, after 1k resistor -140v
    screen voltage on 6146 125v
    resistance on modulation transformer primary 70 ohms, 37 ohms center tap but I notice 7 wires coming from the modulation transformer, not six as indicated on the schematic although two are connected together.
    What are really need are normal voltages as none are on the schematic.

    radio_Johnson_Viking_Valiant_schematic.jpg
     
  2. N2EY

    N2EY Premium Subscriber QRZ Page

    What is the problem?

    What are your questions?

    There are voltage and resistance charts in the Valiant manual. Free PDF download from BAMA.

    PLEASE don't leave a transmitter on when you start to smell something, or it starts to act oddly.

    PLEASE do some RESEARCH into the manuals, schematics, and websites of those who have dealt with the radios you have.

    PLEASE don't bogart. Give as much RELEVANT information as possible, not as little.

    Value the time and effort of others MORE than your own, not less.
     
    Last edited: May 23, 2020
    AC0OB and W4NNF like this.
  3. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    Bold N2EY
    What is the problem?
    Excessive modulator current causes buzz and odor

    What are your questions?
    What causes excessive modulator current

    There are voltage and resistance charts in the Valiant manual. Free PDF download from BAMA.
    I have the physical manual and you clued me in to the tables thus I have work to do.

    PLEASE don't leave a transmitter on when you start to smell something, or it starts to act oddly.
    I don't anymore.

    PLEASE do some RESEARCH into the manuals, schematics, and websites of those who have dealt with the radios you have.
    I have looked at several web sites, most talk about too little modulator current.

    PLEASE don't bogart. Give as much RELEVANT information as possible, not as little.
    I hate that term but it is the price I must pay to get a response.

    Value the time and effort of others MORE than your own, not less.
    I have put in 3 hours so far.
     
    W1TRY likes this.
  4. WR2E

    WR2E Ham Member QRZ Page

    @K1OIK

    Burt, how does R59 look? (cathode metering resistor)
     
  5. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    Not an issue as it is actually drawing excessive current. It already cracked a plate resistor.
     
  6. WR2E

    WR2E Ham Member QRZ Page

    It could be. Possibly the cause of too much current. That's why I asked.

    You know that's the shunt resistor for the current measuring circuit?

    All of that excessive current is flowing THROUGH that resistor! If that current was enough to damage one of the resistors in the plate, it's very possible that the current from BOTH tubes could mess up that resistor.
     
    Last edited: May 23, 2020
  7. WR2E

    WR2E Ham Member QRZ Page

    This looks low. If you follow that line to the left, it says -265

    C93 could be toast.
     
  8. K1APJ

    K1APJ XML Subscriber QRZ Page

    My copy of the manual has a voltage table on page 31 (attached.)

    The schematic you posted shows that the negative supply voltage downstream of the 1K should be -265 V. Look straight down from the keyer tube.

    As a first pass, the bias voltage on the modulator tubes is clearly too low.
     

    Attached Files:

    KD2ACO likes this.
  9. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Is C93 original? If it is, it's at least as old as I am.

    If I was an electrolytic cap, I'd be Methuselah.

    Methuselah.jpg
     
    AC0OB, W1TRY, W7UUU and 3 others like this.
  10. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    @K1APJ @WR2E @N2EY outliar readings FYI:
    v21 bias rectifier résistance pin 4/5 should be 12k ohms is 7k, pin 6 should be 11k ohms is 6k ohms
    v21 bias rectifier pin 4 should be -262v is -170v
    V17 6146 modulator pin 3 should be 218v is 225v pin 5 should be -46v is -33v
    V17 modulator pin 3 should be 50k ohms is 58 k ohms pin 5 should be 2300 ohms is 4200 ohms
     

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