Need DX-40 part -- 40m osc. coil L2

Discussion in '"Boat Anchor" & Classic Equipment' started by K5DH, Oct 20, 2018.

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  1. K5DH

    K5DH Ham Member QRZ Page

    Still in need of a coil, or the specs so I can rewind mine. . . anyone? Buehler? Buehler?
  2. AC0OB

    AC0OB Subscriber QRZ Page

    The 40 meter coil was in actually a variable choke coil with permeability tuning, broadly peaked on 40 meters

    In lieu of any forthcoming data or parts let's make some assumptions.

    The tube specs say the output capacitance is 5.5 pF.

    Lets add another 5 pF for added circuit (parasitic) capacitance so Ct = 10.5 pF.

    The inductance needed to resonate with that for 7.2 Mhz is = 48 uH.

    Put a 47 uH choke ( Ic > 75 mA) in series with the plate lead and see what happens.

    An alternative is the circuit below with a 33 uH coil and a padding capacitor.


    Attached Files:

    Last edited: Nov 4, 2018
  3. AC0OB

    AC0OB Subscriber QRZ Page

    Forgot to quote your post.

    See above.

  4. AC0OB

    AC0OB Subscriber QRZ Page

    I found some additional information after looking through some vintage component catalogs.

    The 40m coil is most likely the Miller 4206 and it is described as having an adjustable inductance of 20-55 uH which makes sense. The Miller 4206 is a single Pi wound choke with one "Pi cake" fixed to a Nylon sleeve with a threaded adjustable ferrite core and looks exactly like the one in the parts list of the DX-40 Manual.

    So the alternative circuit above should work if you cannot find an original coil.

    N2EY likes this.
  5. AC0OB

    AC0OB Subscriber QRZ Page

    Any updates on the coil situation?

  6. K5DH

    K5DH Ham Member QRZ Page

    Haven't looked at it lately. Working on an early production Ten Tec Omni-A, msn 0078, at the moment. I do plan to order that Miller 4206 coil for the DX-40, though. Looks like a good substitute.
  7. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    I offered in message #10 to help and got no response.
  8. N2EY

    N2EY XML Subscriber QRZ Page

    W7UUU likes this.
  9. K5DH

    K5DH Ham Member QRZ Page

    You said "If and only if the others can't help." Phil identified what looks to be a viable replacement which is commonly available at around $5 plus postage. I'll try one of those, and if it doesn't work out, I'll contact you for the real thing. Didn't mean to slight you. Just hadn't gotten to that "if and only if" stage yet.
    W7UUU and N2EY like this.
  10. K1OIK

    K1OIK Platinum Subscriber Platinum Subscriber QRZ Page

    That sounds fair. I think that deal sounds great.

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