Astatic D-104 Restoration - Dynamic Mic Element Recommendations

Discussion in 'General Technical Questions and Answers' started by KJ5XX, Feb 12, 2009.

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  1. KJ5XX

    KJ5XX Ham Member QRZ Page

    Hey All:

    I have an old Astatic D-104 Mic that I'd like to restore. I want to pull out the old Crystal mic element and preamp and replace it with a modern Dynamic microphone element (not a crystal element). I'd use something like a Heil HC-4 or HC-5, but unfortunately Bob Heil has pulled these elements off the market (people were putting them in microphones and then remarketing them as Heil mics).

    Not sure what specs I should be looking for to make the mic compatible with a modern rig with the sort of freq response/impedanance that would work well and have good audio.

    I have a Kenwood TS-570D, and was thinking that an element with a 600 ohm impedance and freqency response from 50hz-15 or 20khz would work, but am unfamiliar with mic sensitivity specifications.

    Found a site with a number of difference choices and would appreciate some thoughts/recommendations on an element that would be compatible or considerations I need to think about.


    Ron - KJ5XX
    Last edited: Feb 12, 2009
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

  3. W9GB

    W9GB Ham Member QRZ Page

    Ron -

    I do not know what you information source is -- DID YOU CALL HEIL ?
    Bob did stop selling the HC-4/HC-5 elements individually, but the element is available as part of the full HC-104 kit.
    You can also use ANY dynamic (Lo-Z) element (even a Kenwood mic element from Kenwood parts) -- as long as you correctly mount it with a baffle int he D-104 head -- for properly sounding audio.
    Mouser and MANY audio/sound reinforcement suppliers have dynamic elements.
    You can even walk into Radio Shack and purchase a 2 or 3-wire elecret mic element (< $5).
    Elecret element require a power source and need to be properly wired.

    The HC104 Element modification kit ($70 USD) for the Astatic D-104 microphone.
    This kit of parts uses the Heil HC element and still listed on the web site

    For questions contact:
    E-mail Bob:
    Heil Sound, LTD
    5800 N. Illinois St.
    Fairview Heights, IL 62208
    FAX 1-618-257-3001
    E-mail the webmaster (edits/corrections) at:
    Last edited: Feb 12, 2009
  4. KJ5XX

    KJ5XX Ham Member QRZ Page

    Yes, I'm aware that he sells this kit, but I'm not interested in the kit, only an element. Don't see the point in paying $30 for a bunch of foam when the elements used to go for $44. I have a couple of Bob's elements that I've used to restore other mics, but they're as rare as hen's teeth these days - unless you want to purchase the kit (which I don't). Nothing against Bob - his stuff is the best, but not willing to pay that price.

    W9GB said:

    Mouser and MANY audio/sound reinforcement suppliers have dynamic elements.
    You can even walk into Radio Shack and purchase a 2 or 3-wire elecret mic element (< $5).
    Elecret element require a power source and need to be properly wired.

    Yes, Mouser has a number of dynamic elements - all of which have different characteristics (sensitivity, etc.). I guess what I'm looking for is advice on how important sensitivity is on choosing a proper ham radio element, and out of the choices they offer, not sure which one would be the best option.

    Could go with an electret element via RatShack, just not sure what sort of audio quality I'd get - just looking for the best solution.


    Ron - KJ5XX
    Last edited: Feb 12, 2009
  5. W9GB

    W9GB Ham Member QRZ Page

    The search for the "best microphone" or "best sound" is like looking for The Lost Chord :)
    IF you desire your voice to be transmitted as it 'actually sounds' -- then a flat response curve from 300-3,000 Hz will be fine.
    Some operators desire emphasis or de-emphasis of the bass (low pitch) qualities or treble (high pitch) qualities of their voice. Some commercial radio announcers prefer specific microphone -- ask AG3Y about "voice talent".
    Poor selections are why some people on the radio sound more like Donald Duck or Darth Vader. :rolleyes:

    As far a DIY, as long as you can find a good sound quality foam and a baffle --
    you just need to properly fit those components (black panty hose can be used) with your new element

    Earlier QRZ Q&A dicussion of D-104 retro-fits

    Steven Fraasch, K0SF
    Adapting the Astatic D-104 Microphone for Use with Modern Transceivers
    August 1999 QST, page 34
    This article is available free for ARRL members

    Joe Carcia, NJ1Q
    More on the Astatic D-104
    March 2001 QST

    George Heidelman, K8RRH
    More on the Astatic D-104
    June 2002 QST

    W8CWE : D104 adapted for Icom 706

    D104 index -- "bookmark" in your browser

    Doug DeMaw, W1FB (sk) FET circuit for D104 - CQ February 1994
    (mentioned in web pages below)


    D104 and Icom equipment

    Last edited: Feb 13, 2009
  6. KJ5XX

    KJ5XX Ham Member QRZ Page


    Ahh, In Search of the Lost Chord - if memory serves me right (which it often doesn't these days :rolleyes: ) was the name of a Moody Blues album.

    Great information! Some of this I already have and some is new to me.

    I did FET/Op-amp conversion of a D-104 a few years ago based on a design by Walt Breining, N9WB. Works great and I use it as my current station mic. I love these old mics though, and restoring them is something that is within my rather limited electronics ability. :eek:

    I own several of them, including an old Astatic DN-20U (similar to the DN-HZ) that I'm restoring, with new hammartone finish, new felt, etc, and just thought I'd try a different approach and try to find a low Z (on the order of 600 ohms) element to replace the old Rochelle Salts crystal element in these mics, thereby eliminating the need for the op-amp circuit.

    The Kobitone crystal element mentioned in one of the posts may be the best answer, but thought there might be options in other mic element types.

    Haven't heard the black pantyhose trick. Will have to give that a try (gee honey, looks like you have a run in your stockings - what a shame!)

    Thanks again Greg for the good info.
  7. W2VW

    W2VW Ham Member QRZ Page

    The Kobitone elements have a lot less low end frequency response compared to a properly terminated, undamaged D-104 element. I have tried several into an MPF-102. Forget it unless you just want to bust pileups.


    Good information - thanks! Have you found one that you like?
  9. KJ5XX

    KJ5XX Ham Member QRZ Page


    Thanks, wasn't aware of that, and I'll ask the same question as above - is there a particular element that you prefer?

    The problem with finding an answer to a question like this isn't that there is no information to be found, it's that there is a LOT of information and not all of it agrees. But, after doing a bunch of reading on the subject (and many thanks to Greg and the other helpful posts here), I'm convinced that if modifying or restoring a D-104 for use with modern rig, there are several options:

    1. If the mic has the "amplified" base (T-UG8 or T-UG9), you should be able to use the mic without alteration - just wire it to match your particular radio.

    2. If the mic has the older, non-amplified (UG8) base, you can build a simple JFET circuit like this one

    3. Replace the old crystal (Rochelle Salts) Astatic element with the Kobitone 25LM022 (assuming the mic has the amplified base)

    4. Replace the element with a Medium-Z (~600 ohms) dynamic element such as the kit available from Heil ($70 US)

    Since the old crystal elements of these mics are sensitive to both heat and shock (such as if the mic was dropped) you may modify the mic only to find that you have poor audio quality. If this is the case, you can always revert to options 3 or 4 above.


    Last edited: Feb 13, 2009
  10. KA9VQF

    KA9VQF Ham Member QRZ Page

    At one point in my life I had a CB shop. I personally don’t like the D-104 mic but a lot of other people did.

    I converted a lot of them to dynamic mic elements as it was pretty much imposable to obtain elements from Astatic.

    I used a dynamic element that was readily available from Radio Shack at the time. It worked well with the little amplifier already in the base of most of the D-104 mic’s I worked on.

    I used plain old Styrofoam sheeting that came in packaging to fill the headshell. Once I had a round piece large enough to fill the mic shell, I just cut a hole in the center and glued the mic element to it with Elmer’s glue.

    I usually put a piece of thin red felt between the mesh of the front part of the mic and the element.

    You need to take care that none of your mounting material or if you use it felt {or even nylon stocking} is touching the front of the mic element. This can cause a muffling to occur.

    My idea was that by using the red felt people would be able to immediately recognize that it was no longer a stock D-104. Besides having the added benefit of masking ‘puff’s’ when the user would talk closely to the element, in my mind, it made the mic more attractive.

    I used a few electret condenser mics in D-104’s too. Usually for folks who really wanted a desk mic for their 2M rigs. Most mobile 2M radios already had a condenser mic in the original mic so it was pretty easy to wire one for it.

    Generally I would remove or disable the amp in the mic stand tho. It was not needed.
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