DX-20 Questions

Discussion in '"Boat Anchor" & Classic Equipment' started by W7AMI, Dec 13, 2019.

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  1. W7AMI

    W7AMI Ham Member QRZ Page

    I have a Heathkit DX-20 that has an open 1.1 mH inductor. The one on the cathode of the oscillator tube that goes to the key jack. I don't have another 1.1 MH inductor and the pi wound ones that I have found on-line cost almost as much as the radio did. I do have a 2.5 mH pi wound inductor at hand. Does anyone know of a reason that this won't work? I assume the inductor is there to block the RF from the oscillator from going out to the key while providing a path to ground for the DC current. I guess that it would also be part of the key click filter? Thoughts anyone?

    Terry W7AMI
  2. KP4SX

    KP4SX Premium Subscriber QRZ Page

    Hi Terry,
    I have some NOS 1.0 MH pi-wound chokes if that might help. What is the current rating?
    (no charge)
    If its part of a key click filter it may be that the DC resistance is an important number for timing. Just a thought.
  3. K9STH

    K9STH Ham Member QRZ Page

    The r.f. choke is not part of any key click filter.

    Other manufacturers, using the same, identical, crystal oscillator circuit using the 6CL6, use 2.0 mH, 2.4 mH, and 2.5 mH chokes. Heath probably got a really good deal on 1.1 mH chokes and used them in the DX-20 and DX-40 transmitters. The choke can be replaced with any r.f. choke with a value at least between 1.0 mH and 2.5 mH and probably an even larger range of values and should work fine. Basically, it doesn't make a "hill of beans" difference.

    The 2.5 mH r.f. choke was used in quite a few home-brew projects described in all sorts of amateur radio magazines, the ARRL Handbooks, etc., in similar applications.

    Heath was notorious for using whatever part that they could obtain, at the lowest price, that would work in the circuit. Basically, they did everything possible to keep the cost down while still providing a product that would do the job.

    Glen, K9STH
  4. W7AMI

    W7AMI Ham Member QRZ Page


    Thanks for the correction and the information. So it looks like I can use the 2.5 mH inductor I have in hand then. That's good to know.


    Thanks for the generous offer of an inductor but it looks like I'm good to go.

    Terry W7AMI

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