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Home Brewing An Astatic D-104 Head Into a Ring Mic

Discussion in 'Amplitude Modulation' started by WO4K, Sep 17, 2019.

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  1. WO4K

    WO4K XML Subscriber QRZ Page

    On another thread (see Post Some Photos of Your AM-Centric Rigs) in this AM forum I was asked how I made an Astatic D-104 head into a ring mic. I didn’t want to hijack that thread, so I am posting the information here.

    I made the ring mic back in 2014 for my first AM transmitter, a Heathkit DX 100B. I’m tall and I wanted the mic at my head level, so I didn’t have to bend over to speak into it. Yeah, I know, a ring mic is not of the DX-100B era. I still wanted one.

    First, the donor D-104 head was nothing special. I just found a good D-104 with nice chrome at Orlando Hamcation. I also had a NOS Astatic crystal element.

    All the parts for the ring came from my local Ace Hardware Store. Those parts included two packages of eye screws, springs, a piece of half inch wide aluminum stock for the ring, a foot long piece of PVC sewer pipe (the form for the ring), a piece of thin sheet metal stock and a common 4” x ½ inch chrome shower head pipe. Oh, yeah...and a package of JB Weld epoxy.

    The aluminum stock was cut and formed around the piece of PVC sewer pipe with a hard rubber mallet until I had the ring. I improvised a triangular U-shaped piece from the sheet metal using a hacksaw and a vise (as a metal brake) to create a device to hold the ends of the ring together and mount it to the boom.

    At that point it was just a matter of drilling holes where needed in the ring, hanger and mic. I had a drill press, a small cheapo Harbor Freight job. It became painfully evident that it was not up to the task, so all drilling was done with a hand drill. You can see that I missed getting the two holes at the connector neck and the one at 6 o'clock exactly symmetrical. That's why they call it AMATEUR radio. Once the holes were done I screwed in the eye hooks, setting both sides of the ring in epoxy. I also used the epoxy to secure the eyehooks on the inside of the mic head. A day later I used a file and sandpaper to get the smooth out the outside of the ring and to better shape the hanger. A little spray paint and it was done.

    The boom was from a common old industrial lamp, probably from the 1940’s or 50’s, bought on Ebay.

    That’s it. The whole thing took two days to homebrew. Most of that was spent filing and sanding after waiting for the JB Weld to set. Easy peasy.

    Bud WO4K

    Mic installed.jpg D-104 Conversion.jpg

    ring mic.jpg

    D-104 Element.jpg

    Lamp arm.jpg
    SM0GLD, KA0HCP and W1TRY like this.
  2. WB2GCR

    WB2GCR Ham Member QRZ Page

    Nicely done.

    Since I have other tools, I'd have done it a bit differently, but this is very nice.

    Interestingly, I happen to have the same lamp! It's a machinist's lamp, and mine came
    attached to a Bridgeport mill. Not enough light for me, so it was pulled instantly
    and replaced with an entirely different lighting method. So, maybe it will be in the
    future some sort of microphone arm!

  3. K5UJ

    K5UJ Ham Member QRZ Page

    Thanks for the write-up Bud, I guess I never considered using aluminum flat stock for this. Good ideas.
  4. K4KYV

    K4KYV Subscriber QRZ Page

    Not to in any way denigrate your efforts, I'll have to say that to a purist, a "modern" D-104 will never be made to look exactly like an original ring-mounted mic head. Firstly, vintage heads are approximately 1" thick; the later productions (post-1937) are noticeably thinner, about 13/16" thick. The knurling pattern on the rim of the front and back pieces are noticeably different; the original appear machined, while the later productions are less distinct, formed from a mould. The originals did not have the 3-prong plug on a detachable head. The cable was permanently attached to the head internally, using a small cable clamp, with cord coming out of the head through a hard rubber or bakelite bushing. The heads to the screws holding the clamp are visible on the back plate. Not immediately obvious, but the spring hooks on the original heads are not spaced uniformly 90° around the head. The hooks are closer together from the two sides of the head and farther apart from the top and bottom, although the ones on the ring are usually 90° apart. Spacing them exactly 90° on the mic might not have allowed the bases of the hooks to clear the sleeves inside the head over the four screws between the front plate and back plates, that hold the mic head together.

    On the original, when mounted the conventional way with 8 springs, like what you have, the cord comes out about 45° to one side, not straight up and down. This is avoided by using 4 springs, each attached straight between the hooks on the mic head and ring, extending out radially. Old style double-button carbon mics were mounted both ways.

    When the D-104 first came out circa 1933, they were all designed to spring-mount in a ring. Probably made to work as a drop-in replacement for a double-button carbon.

    Another way, instead of using springs, is to mount using some kind of black fabric cord. This is shown in some of the early Astatic ads . I did a variation of this in mine using thin black shoe laces, copied from a 1935 video from the Netherlands. Close-up views of the mic are seen at 1:10, 2:14 and 3:30.

    Here are some photos. Click on each image to expand to full size.
    Boom mount in ring closeup.JPG Boom.JPG D-104.JPG D-104_grommet.JPG Desk mic.JPG Old D-104.jpg rear early.JPG
  5. K5UJ

    K5UJ Ham Member QRZ Page

    Don thanks for the photos. I had forgotten that you had yours mounted in a spring ring. I found a source for that elastic cord that can be used for microphone suspension cord. There's a chain of craft stores called Jo Anne and there's one not far from my house. They had it in various widths. I had forgotten all the subtleties of the original D104 head. No other microphone can wake up a classic AM rig the way the D-Wonderful can. Of course, opinions vary:
  6. N2DTS

    N2DTS Ham Member QRZ Page

    If you are just going to plug a mic into a rig without any fancy processing, I can't think of a better sounding mic in general.
  7. K5UJ

    K5UJ Ham Member QRZ Page

    Agree. So many ham rigs seemed to have been made with the D104 in mind. However, Turner and others made xtal element microphones and they might be equally good for all I know. Interestingly, Astatic made other mics using crystal elements but I never see them for sale except for the JT30. They made a line of beautiful chrome mics that used 2 to 4 crystal elements inside the microphone head but these must be extremely rare. I've never seen one but i believe Skip K7YOO has or had one.
  8. VA3EE

    VA3EE Ham Member QRZ Page

    All I can say is AWESOME job.
    I have a bunch of D104 mics and am going to use one to do this and another to make a lamp.
    Very nicely done.
    Cheers Donnie VE3GNX
  9. W7TFO

    W7TFO Platinum Subscriber Platinum Subscriber QRZ Page

    If any of you doing such a project need a period-correct cord bushing, I have threaded Bakelite ones to pass up to a 1/4" cable.

    Your addy and I'll mail you one.

    W1BR, KD2BRM, K4KYV and 1 other person like this.
  10. K4KYV

    K4KYV Subscriber QRZ Page

    If you dismantle a working D-104 to make a lamp or replace the stock element with, for example, a low impedance electret condenser element, please don't destroy or toss out the original if it still works. Since they are no longer manufactured, every one of these that is destroyed means one less on the face of the planet, for ever. Those who still use these mics in their original condition are always looking for a source of replacement elements. Give them away, sell them or trade them; just make sure that any good element taken from a working mic is handled with care and finds a new home.

    A few months ago on another forum, someone boasted about how he had acquired a bunch of used D-104s from hamfests and estate sales, "upgraded" them by polishing them up and replacing the original crystals with dynamics or electrets, and then re-sold them on eBay. When asked what he did with the originals, he replied that he had torn apart a few to see what was inside, and tossed the rest in the trash... For shame!

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