DX-60 Initial Test Problem - Tune Level and Final Tuning Problems

Discussion in '"Boat Anchor" & Classic Equipment' started by W1FMX, Jul 30, 2021.

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  1. W1FMX

    W1FMX Ham Member QRZ Page

    I have re-capped a DX-60 and replaced any bad resistors. When I do the initial test, the Tune level needs to be turned down to 1 (i.e., all the way to left) to get a maximum reading on the meter. It will go up to 2.5 easily when I adjust the Drive Level, but the Tune level control right has to stay at 1 for the meter to peak. Then, when I move the switch to Plate and turn the knob to AM, the meter pegs to the right and moving the Final Tuning knob will not dip the meter reading. Any suggestions? Thanks.
     
  2. VE3CGA

    VE3CGA XML Subscriber QRZ Page

    this video is very good for tuning a dx 60, audio is low though
    If you have a manual there should be voltages on the schematic to check
    Are you tuning up on a dummy load or antenna?
    Something might be off in the output tuning if you have the loading at minimum and cant get a dip on the plate tuning
     
  3. N2EY

    N2EY Ham Member QRZ Page

    @W1FMX

    What crystal are you using for the test?
     
  4. W1FMX

    W1FMX Ham Member QRZ Page

    Thank you for the reply. I will look for the video and at the output tuning. I do have the schematic, so I will check the voltages as you suggest. I was tuning into an 1.5 kW MFJ dummy load. 73's,

    Bill W1FMX
     
  5. W1FMX

    W1FMX Ham Member QRZ Page

    I tried the two crystals that I have - one is for 80M ( 3885 kc) and the other for 40M (7240 kc)...problem was the same on both bands/with both crystals.

    Thanks.

    Bill
    W1FMX
     
  6. N2EY

    N2EY Ham Member QRZ Page

    Are the crystals actually oscillating? Can you hear the signal on a receiver?
     
  7. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Suggestion:

    Very important: Never let the Final's grid current exceed 3 mA. Use the "Driver Level" control to keep the grid from exceeding this current.

    There is an 18k resistor (Brown-Grey-Orange) in the grid of V2 that connects to the choke coil in the grid circuit - put a DMM across this resistor.

    This assumes you have checked the crystal socket connections to the crystal switch and V1 as well.

    Put a 40 meter crystal in the X1 position and during Keydown adjust the L1 core for a maximum negative voltage using an insulated or plastic tool. If adjusting L1 does not change the negative (bias) voltage here, then check L1 and its wiring for continuity.

    Pheel
     
    Last edited: Jul 31, 2021
  8. W1FMX

    W1FMX Ham Member QRZ Page

    Hi, Pheel.

    Thank you for the input.
    I checked the 18K resistor and it is about 16K, so it is not high.
    Checked the crystal sockets and there is continuity on each leg when switched. Also, there is continuity to C1 and Pin 2 on V1.
    All the voltages on V1 check out o.k.
    There is no detectable signal on a receiver.

    But, on V2 I find the voltages are really off:
    at Pin2 voltage is -200 (should be -115); voltage at Pin 6 is 175 (should be 200); voltage at Pin 8 is really off: it is 100 (should be 12). I checked R6 and it is o.k.

    So, I guess there must be a short that I need to find that is causing the higher voltages on V2.

    73's,

    Bill
     
  9. N2EY

    N2EY Ham Member QRZ Page

    If there is no detectable signal on a receiver, the oscillator stage isn't oscillating, so that's the thing to fix first.
     
  10. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    What is the voltage "across" the 18k on Keydown?

    1) The voltage on V2 Pin 8 varies with the Drive Level setting. It should change when you move the knob because it is connected to B+ via a 6.8k 2W dropping resistor.

    2) Check the 1k 2W that feeds the plate of V2.

    3) Here's the deal. This transmitter has grid block keying which means that on Keyup there is a negative voltage that forces the grid voltages to go more negative cutting the tubes off.

    For example, on Keydown, the voltage at the junction of R1 and R2 should go from about -83V to 0V.

    I.e., we need to make sure this bias voltage at the junction of R1 and R2 goes from about -83V on Keyup to 0V on Keydown. If not, check continuity from the Key through to the Function Switch contacts.

    Also, make sure there is a 1/4" Key plug in the Keyjack so as not to key the transmitter by accident since it is a 'shorting' jack.

    Pheel
     

    Attached Files:

    Last edited: Jul 31, 2021

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