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Need help with Drake TR-4CW

Discussion in '"Boat Anchor" & Classic Equipment' started by N8PWM, Mar 10, 2019.

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  1. N8PWM

    N8PWM XML Subscriber QRZ Page

    Hi all! I am now the proud owner of a TR-4cw with the remote vfo and 500 Hz filter.

    The rig is in need of some help. I cannot get the carrier oscillator to adjust (C129) so that usb and lsb sound the same. LSB is very high pitched and tinny sounding and usb is very low and muffled. No matter the adjustment of the cap they are not close. I have tested all the tubes and all are in excellent condition.

    I am brand new to Drake gear and have wanted some since I was licensed in 1976. This is a good project since it does work but needs a bit of TLC.

    I am looking for suggestions on what to check and where to start. I hesitate to do a complete recap if I don’t have to. I prefer to start with the simple stuff.

    Thank you,

    Craig N8PWM
     
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    A recap is unlikely to help with your carrier oscillator problem.

    It sounds like the carrier oscillator crystal or associated capacitors has drifted so far off frequency that the trimmer cap won't pull it back to where it belongs. Do you have access to an accurate frequency counter? If so I'd check the oscillation frequency and you'll likely find it's not close to the desired frequency.

    You could also have a problem with the relay that switches in the extra capacitance to shift the carrier frequency for CW transmit use. If that extra cap isn't bypassed to ground by the relay the carrier oscillator won't adjust properly. You can test this by temporarily shorting the C04, R141 junction to ground and seeing if that changes your ability to center the carrier oscillator. If the relay is properly shorting C04 to ground when in USB or LSB modes then nothing will change, if your tuning shifts with the shorting wire in USB or LSB modes then you've got a relay problem such as dirty contacts or the relay isn't operating properly. The easy test would probably be to connect a clip lead to the C04, R141 junction and leave the far end free. Turn the rig on and listen to USB or LSB received audio tone and tap the free end of the clip lead to ground, if the pitch changes then the relay isn't dragging that connection to ground as it should.

    Conceivably you could have an issue with V16 such as someone swapping in a substitute tube with different interelectrode capacitance as that might also shift the carrier oscillator frequency. I'd check component values around C16 to make sure you don't have any way out of spec resistors but if everything checks out and the carrier oscillator can't be balanced for near equal USB/LSB recovered audio pitch then your 9Mhz crystal has probably drifted and should be replaced.
     
    K2XT and N2EY like this.
  3. WA5VGO

    WA5VGO Ham Member QRZ Page

    The trimmer capacitor could be bad. If you have a frequency counter, loosely couple it to the carrier oscillator and check the frequency. It should be possible to move it a little above and below 9MC. If you can do this, you probably have a bad filter.

    Darrell
     
    K7TRF likes this.
  4. W8CF

    W8CF Ham Member QRZ Page

    Craig

    Every Sunday at 4:00EST on 7.238 there is a Drake Technical net. Most of the moderators and technical experts are in the midwest (mostly Ohio). I am in northern Michigan and usually hear most of them. They are very helpful.

    Rick W8CF
     
    K3XR likes this.
  5. N2EY

    N2EY Premium Subscriber QRZ Page

    A bad filter is doubtful because the TR-3/4 family use different filters for USB and LSB, but the same carrier crystal. Since both USB and LSB are affected, and in opposite ways, it points to the carrier oscillator being the problem.
     
    K2XT likes this.
  6. DJ7TL

    DJ7TL Ham Member QRZ Page

    I think the solution is a new 9Mhz crystal. I had the same problem with my Drake TR-4 and changed the crystal.
    This was 5 years ago and the Transceiver works witout any problems.

    73, Joerg DJ7TL
     
  7. K3XR

    K3XR Ham Member QRZ Page


    Looked at the title of this thread and after reading found it seemed like the identical problem I am having with my TR-4cw/rit. Rig was working great and developed poor sounding audio. Checked some tubes and made some other checks and no luck. I also have an older TR-4C that has a few problems. This afternoon placed both rigs on the bench and swapped the 9 Mhz crystal from the TR-4Ccw/rit with the TR-4C. As Joerg indicated that solved the problem...bad crystal. Many thanks Joerg and others that replied to the thread. Craig, hope that solves your problem. Next, I guess, look for a source for a new crystal to replace the bad one. My experience with Drake receivers over the years is that if they have less than good sounding audio...there's a problem.
     

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