Drake TR4 loads on 80m & 20m but not on 40, 15, or 10

Discussion in '"Boat Anchor" & Classic Equipment' started by KG5TW, Feb 6, 2020.

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  1. KG5TW

    KG5TW Ham Member QRZ Page

    I am a resurrecting my old TR-4 after many years of sitting in storage. When tuning it thru a 50-ohm cantenna dummy load, I find that it works perfectly on 80m and 20m with full rated power output and very normal RF Tune, Plate, and Load settings. However, it will not load up at all on 40m, 15m, or any of the three 10m segments. I have run all the switches back and forth many times to "shine up" the contacts but to no avail.

    The radio was working fine in all respects when I took it out of service about 9 years ago.

    Any advice welcome and much appreciated.

    Charlie
    KG5TW
    Llano, Texas
     

    Attached Files:

  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Does it receive normally on 40m, 15m and 10m with full sensitivity? IOW, could you have a heterodyne crystal problem or a crystal switching problem on those bands? You might try unplugging and then plugging the het crystals back into their sockets or cleaning the switch wafer that selects the crystals for each band.

    Have you tried peaking the drive stages per the alignment instructions?
     
    WA1GXC likes this.
  3. WA1GXC

    WA1GXC Ham Member QRZ Page

    Charlie, Mr. TRF gave you the answer in the post above. Drake rigs have a clever and complicated

    signal mixing architecture. You most likely have a bad tube and if you're lucky, nothing worse.

    80M and 20M utilize one signal-source less than on other bands. Read the 'Theory' section carefully

    for the background necessary to do future work.

    When you fix your receiver, the transmit functions will immediately spring to life.

    As a tip, de-activate the high-B+ in the power supply so you can work much more safely on the

    receiver section and receiver alignment. A 250V slip is way better than 650V at 500 mA.


    My dead-on-arrival TR-4C had exactly the same symptoms.

    You've got 3 oscillators - PTO, band-heterodyne (with all the many xtals) and a fixed-freq. osc

    at around 5 MHz. The entire Pre-mixer circuit is not utilized on 80 and 20. Replace

    both 6EA8 tubes for your first lottery pick.

    Add'l general knowledge on the TR-4 see WB4HFN and VE3EFJ Drake sites for future issues.

    Beautiful radio. G L !


    I was working fine in all respects 9 years ago, too. The Universe has other plans.
     
  4. KG5TW

    KG5TW Ham Member QRZ Page

    This is fabulous information.

    As a mechanical engineer, some of the tests you suggest might stretch my capabilities, but it will be easy enough to clean that switch wafer, unplug and reseat crystals, and replace those two 6EA8's. If that doesn't work, I'll check the two referenced sites and dig deeper. This is a flat-footed re-start with no antenna yet so evaluating receive is something I can't do yet. I'll have a 51' crank up, A4S, and 160m-20m EFHW up in the next two or three months so I expect to be able to do a better job of evaluating matters if I haven't figured it out otherwise by then.

    Thanks again for the great info and the compliment on the radio!

    73
     
  5. W1VT

    W1VT Ham Member QRZ Page

    If you have a general coverage receiver you may be able to listen for the oscillators.
     
    WA1GXC likes this.
  6. N2EY

    N2EY Premium Subscriber QRZ Page

    DON'T just dive in and start cleaning, realigning, replacing!

    BEFORE you do anything, try the following:

    Put the rig on 20 and turn on the calibrator. You should be able to hear the calibrator signal on the 100 kHz points without an antenna.

    Then switch to 40 and see if you can hear the calibrator on the 100 kHz points on that band. Same on 15 and 10.

    Then get a length of wire, the longer the better, and connect it to the center conductor of the antenna jack of the rig to act as a receive-only antenna. Tune around on 80/75 and 20 and you should hear some signals, proving the receiver and "antenna" are working on those bands.

    Then switch to 40, 15 and 10 meters and see if you can hear anything on those bands. 15 and 10 may appear dead, though.

    If 80 and 20 work but 40, 15 and 10 don't, it's probably the heterodyne oscillator. Try swapping the 6EA8s and unplugging/replugging the heterodyne crystals (one at a time so you don't mix them up).

    73 de Jim N2EY
     
    VE2GCE likes this.
  7. KG5TW

    KG5TW Ham Member QRZ Page

    Jim, thank you for this. I do in fact want to "sneak up on this" and you've given me the recipe to do so. Much obliged. Last thing I want is to make things worse!

    You guys have all been great and I truly appreciate it!!

    I'll let you know what happens. It will be a few days.

    Charlie
    KG5TW
     
    N2EY likes this.
  8. AD4U

    AD4U Ham Member QRZ Page

    In my 50+ years as a ham, 6EA8 tubes have caused me a lot of problems. IMO the 6EA8 has the worst failure rate of any other tube.

    Dick AD4U
     
  9. WA1GXC

    WA1GXC Ham Member QRZ Page


    Hi Charlie--
    Two quick thoughts.

    1. Sorry--Brain-fail/Dogzheimer's-- I stated there is a fixed oscillator at 5 MHz. It's at 9.0 MHz .

    9.0 MHz + 5.0-5.5MHz PTO = 14.0 -14.5 MHz
    9.0 MHz - 5.5-5.0 MHz PTO = 3.5 - 4.0 MHz

    The T-4X series gear has fixed osc. at 5.6 MHz- -regret the confusion.


    2. If replacing the 6EA8's doesn't get you the heterodyne oscillator back to life, try this simple
    next step-- The heterodyne multiple-crystal board assembly has ground return to chassis lug. As with
    many other chassis-common returns, after 50years there's oxidation, and a common return can show
    <1 on an ohmmeter but it is a bad ground at RF. Back-out the screw 1/2 turn, squirt it with contact
    cleaner and/or De-Oxit and re-tighten. This is good maintenance practice anyway absent even a
    specific problem.

    GL OM


    73
     
    N2EY likes this.
  10. N2EY

    N2EY Premium Subscriber QRZ Page

    Actually, the PTO in the TR-3/4 has a 600 kHz range. This was done so that 10 meters could be covered in three 600 kHz ranges rather than four 500 kHz ranges.

    For the bands other than 20 and 80/75, the PTO signal is mixed with the signal from a heterodyne crystal oscillator to generate the needed conversion frequency. If the heterodyne oscillator fails, 20 and 80 will still work, but the other bands will be dead.

    Here's the entire scheme:

    80/75: 9.0 MHz - 5.5-4.9 MHz PTO = 3.5 - 4.1 MHz

    40: 21.5 MHz Het Osc. - 5.5-4.9 MHz PTO = 16.0 - 16.6 MHz Premixer Output
    16.0 - 16.6 MHz Premixer Output - 9.0 MHz = 7.0 - 7.6 MHz

    20: 9.0 MHz + 4.9-5.5MHz PTO = 13.9 -14.5 MHz

    15: 35.5 MHz Het Osc. - 5.5-4.9 MHz PTO = 30.0 - 29.4 MHz Premixer Output
    30.0 - 29.4 MHz Premixer Output - 9.0 MHz = 21.0 - 21.6 MHz

    10A: 42.5 MHz Het Osc. - 5.5-4.9 MHz PTO = 37.0 - 36.4 MHz Premixer Output
    37.0 - 36.4 MHz Premixer Output - 9.0 MHz = 28.0 - 28.6 MHz

    10B: 43.0 MHz Het Osc. - 5.5-4.9 MHz PTO = 37.5 - 36.9 MHz Premixer Output
    37.5 - 36.9 MHz Premixer Output - 9.0 MHz = 28.5 - 29.1 MHz

    10C: 43.6 MHz Het Osc. - 5.5-4.9 MHz PTO = 38.1 - 37.5 MHz Premixer Output
    38.1 - 37.5 MHz Premixer Output - 9.0 MHz = 29.1 - 29.7 MHz

    Note that all the bands except 20 tune in the same direction - which is opposite the direction the PTO tunes.

    The TR-3/4 uses two crystal filters, one above and one below the 9 MHz carrier oscillator. Which crystal filter is used for which sideband depends on the band in use, due to sideband inversion on some bands. That's why the sideband selection switch isn't labeled "USB - LSB" and there are indicator lights to tell you what sideband you're using.

    73 de Jim, N2EY
     
    K7TRF likes this.

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