Replacement for D-104 element?

Discussion in 'Microphones, Speakers & Audio Processing' started by WA8LGM, Jun 6, 2020.

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  1. K5UJ

    K5UJ Ham Member QRZ Page

    How high is "high impedance?" Xtal elements worked great with rigs that had 5 or more megaohm input impedance. Ham rigs with inputs down to around 1 meg used D104s. It's fine to replace a crapped out element with something else if the something else provides a rough match to whatever transmitter is used, and the xtal element is truly crapped out.

    As other stated, my experience is that if you want a good xtal element for a D104, you pretty much have to go to hamfests and buy D104s. Other elements don't work as well. I have a pair of those small Astatic lavalier mics--I bought them at a hamfest thinking they would have good elements and they did, but the size of the diaphragm is about half the area of a D104 element and they didn't sound all that great.

    You can go two ways at a hamfest: If you can't test the mic on the spot, look for bargains where you can pick one up for twenty dollars. I don't mind risking that on an untested mic., but $70 or more? No. Alternatively you can put together a small solid state amp and speaker that can run on a battery and a 1 meg input so you can connect the mic using clip leads and try it right there. Another method uses a battery powered solid state oscilloscope. A xtal element can drive the high impedance vertical input of an oscilloscope.
     
    KB0MNM likes this.
  2. KB0MNM

    KB0MNM Ham Member QRZ Page

    I would suggest that you contact W2NER, who has an ad in the swapmeet for a D104 which was modified. Why re-invent the wheel? There have been a lot of folks who had the same D104 microphone problem which you describe. If you had a big collection of QST magazines, there was an article in there around 10 years ago with details for replacement of the original element with a newer 'electret' microphone element. Be aware that most of these have a built-in field-effect transistor which would also require around 8 volts at a small ( really tiny ) amount of current to amplify the signal inside before passing it on. Some sources of these elements would be: PUI Audio ( sold by Digikey, Mouser, and others ) and Tandy. Yes, there is still one Radio Shack store in Brenham, Texas that has not closed. There is also a Tandy website, something like www tandy com. I have no financial interest in the manufacturer PUI Audio, nor in the value-added resellers DigiKey ( www digikey com ) or Mouser. I did once work during the holidays and during my off-duty hours at a Radio Shack store in Memphis. At that time, the price for the element you seek was around $2.50 plus tax. You may wish to check with any mail-order supplier about the cost of shipping. The kit mentioned earlier would likely be easier, and more complete. Many folks suggest new foam and cabling- I have seem a few microphones at hamfests with badly cracked insulation on the cabling. BTW- I do not know W2NER, and would suggest that you let him know your intent before long in any conversation. After all, he appears to be looking to sell a D104, and maybe the 'spare' element he suggested which was still working.
     
    WA8LGM likes this.
  3. KB0MNM

    KB0MNM Ham Member QRZ Page

    Re: K5UJ post #11, I have seen folks use an amplifier based on a 2SC1815 transistor and LM386 intergrated circuit chip, "Mini Speaker Amplifier Cat. No. 277-1008B" which uses a 9VDC battery to test microphones at hamfests. This was an Archer product, and may still be available through the Radio Shack ( Independently-owned ) store in Brenham, Texas or through the Tandy Corporation. They are sometimes found at hamfests, though many of us would not wish to re-sell them due to the utility of a small test amplifier. The parts count is low- a 5K pot with an on-off switch, 6 small 10 uf electrolytic capacitors, 2 mylar capacitors, 6 resistors, a 16 ohm .25W speaker, a 9VDC battery clip, and two jacks. The whole amp is almost small enough to put in a coat pocket- yet would not fit in most shirt pockets. You could build your own using a design found in the Forrest Mimms book entitled "Engineer's Notebook".
     
  4. W1VT

    W1VT Ham Member QRZ Page

    http://kt4qw.com/condenser.htm
    Homebrew Condenser Microphone

    This is the large diaphragm studio style condenser microphone I built from scratch. Gets the "Big Sound" without expensive equalizer-processors. A good inside project for winter.

    Perhaps there is a way of adapting this homebrew microphone project to your needs?
     
    WA8LGM likes this.
  5. KB0MNM

    KB0MNM Ham Member QRZ Page

    Yes, it seems from your profile ( previous posts ) that you want this for a Ten Tec Omni D. There is another operator not too far away ( Kentucky ) who reviewed the radio on eham, and you might get some clues from him:
    73w4udx@gmail.com
    That would be the listed e-mail for W4UDX. According to his bio, an e-mail might work better than a telephone call- a hearing issue. As to the alternative element, the kit suggested earlier would be faster- yet the do-it-yourself project *might* be less expensive ( depending on your junk box and how you value your time ). The project has good technical detail regarding the difference between 'true condenser' and 'electret' elements, as well as an informative set of schematics for amplifiers. If you were to look at the cardboard backing for an old Radio Shack electret, you would find that the field-effect transistor is 'built in' to the assembly. It seems that the MPF102 is one of the most common means of providing immediate amplification / conversion for many of these. The bias voltage is also explained. In short, even if you buy the kit- if you want to know more about microphones- the project is good reading.
     
  6. WA8LGM

    WA8LGM Ham Member QRZ Page

    Sometimes, Murphy gets you and sometimes you get Murphy. I rewired that old D104 with its TUG8 stand. I finally gave up on replacing the element in the mic, bought another had-held mic and kept it for field day.
    I ordered new cable for the mic and a TRS connector for the mic. Kluged it all together and took it to the Field Day sight.
    When I plugged that mic into the OMNI D, I had left the radio in VOX mode and powered it up. When the mic keyed the transceiver, it surprised me that it worked. I called another station on the air and he told me that my audio was right up there where it should be.
    I used that mic for field day and it is sitting on my table right now, fully functional. Sometimes, you just get lucky.
     
    W1VT likes this.
  7. WA8LGM

    WA8LGM Ham Member QRZ Page

    That is one of the nicest home brew projects I've seen in a long time. Very nice.
     
  8. WA8LGM

    WA8LGM Ham Member QRZ Page

    Tom: I remember reading about either a ceramic mic or a variable reluctance mic in somebody's article, but I found it once and couldn't find it again. Any ideas?
     
  9. KF4ZGZ

    KF4ZGZ Ham Member QRZ Page

    BTW- I noticed no one mentioned W2ENY and his stuff.
    He make a kit to replace bad D104 elements.
    Google his call for more info.
    Of course you now have a "lollipop" case with a modern non-D104 sounding mic ..... but at least it's a working mic.
     
  10. WA8LGM

    WA8LGM Ham Member QRZ Page

    Well. Sometimes things work out for the best --- especially by accident. I rewired the T-UG8 base using ribbon cable from an old drive cable. Got a brand new piece (6 ft.) of mic cable (single shield with two wires inside) and a TRS 1/4 inch plug. Cobbled them together and placed the "questionable" D-104 mic into the top plug on the stand.
    I then hooked it up to the radio, not expecting too much.
    I then put a dummy load onto my transceiver and keyed it.
    I was pleasantly surprised when the old "questionable" D-104 worked like a brand new one. I checked out the audio from the mic on another receiver and after confirming that the audio was just as good as it was supposed to be buttoned up the set up and I was ready for field day.
    So, this is to thank all of you who offered me some good ideas as to how to replace the element.
    I think that I got lucky in this one. Well, now the bloody thing works. And I also have (bought it on eBay) another hand mic (Dynamic Hi-Z for a Ten Tec Paragon) extra to use with the Ten Tec Omni D. You know, just in case the old D-104 quits working some day. 73! all.
     
    Last edited: Jul 8, 2020

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