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D-104 Modification By N9WB

Discussion in 'CB Radio Modifications' started by Shadetree Mechanic, Jan 11, 2019.

  1. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    I just found this again going through my documents. The modifications by N9WB are interesting and I was wondering if anyone has done his mods or have heard of anyone doing them. Any and all comments are welcome.
    Chris



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  2. Dmans

    Dmans Well-Known Member

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    Chris,
    Thanks for the link. I have not done this mod and do not currently own a D-104 but this information makes me want to find one to modify!

    73's
    David
     
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  3. loosecannon

    loosecannon Sr. Member

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    yep.

    I do this mod to D104's and have for a while now.

    it works great, and really opens up the bass response.

    I will say however, that the gain is a bit less than the stock two transistor amp.
    It has never been a problem, but if you are someone who is used to the sound of a cranked D104, then you will notice it doesn't get as loud.

    as far as voice articulation and fidelity, i get more compliments with this setup in my silver eagle than i ever did before.

    LC
     
  4. loosecannon

    loosecannon Sr. Member

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    the other tip i like to give out for D104's is that the rochelle salt element in the mic head is attached to the convex foil with wax.

    over time this wax can dry out and temperature variations can cause it to lose its 'purchase' to the foil, causing a tinny sound or low output.

    the cure is to re-melt the wax. i use a lighter to heat up a small screwdriver tip, and press the wax back into the foil. you just have to be careful not to apply too much heat for too long of a time.

    again, i do this to all D104's that cross my bench. it makes me cringe to think of all the MC320 elements that have been pitched in the trash can over the years because of this simple issue.
    LC
     
  5. 357magnum

    357magnum Sr. Member

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    Thanks for sharing LC , now I have to check my Silver Eagle after many years of use . I never knew this ! I switch heads depending if I'm chatting on AM or SSB does this apply to a 10-DA head also ?o_O
     
  6. undertaker

    undertaker Undertaker

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    Hey Leo do you have to turn the mic gain up when using the 10- da head? I notice on ssb it does not move the meter much on the 2000...
     
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  7. 357magnum

    357magnum Sr. Member

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    No Bobby I don't usually touch it but if I do it might be down a " Tad " according to my modulation meter . I try to stay @ 100 percent . My amp doesn't like being over driven .:LOL:
     
  8. 357magnum

    357magnum Sr. Member

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    My settings on my 2K , D-104 opened 1/3 , mic gain set @ 9-10 o'clock depending on what mood I'm in . No more at least on my radio .:ROFLMAO:
     
  9. undertaker

    undertaker Undertaker

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    Thanks Leo I run barefoot but I have a texas star 250 I just never use it...
     
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  10. snow bird

    snow bird Member

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    Thank you L.C I just fixed two of my old mics you help me with out knowing it .
     
  11. loosecannon

    loosecannon Sr. Member

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    glad to hear this info is helping keep D104's alive!


    LC
     
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  12. SIX-SHOOTER

    SIX-SHOOTER Well-Known Member

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    My Silver Eagle with the 10-DA kicks but on my ICOM 746. It sounds Awesome and the mike gain is about half way on the microphone & on the radio. I currently own (30) Astatic D-104 desk microphones & wish I had at least (30) more. They are my all time Favorite microphone. {:>)

    SIX-SHOOTER
     
  13. Shockwave

    Shockwave Sr. Member

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    These types of modifications do wonders at increasing the bass response of a good D-104 element. The input impedance to the pre-amp is what controls the bass response. You can add a 2.5 meg or 4.7 meg ohm pot across the gate to ground if you want to adjust (reduce) the bass.

    Some other things to keep in mind are the 4700 ohm output resistor in this schematic is not the best match for replacing a 500 ohm dynamic stock mic. Many modern rigs use a 1k ohm pot as the mic gain and input impedance resistor. Meaning about 80% of the AF voltage is dropped or lost in the 4700 ohm resistor. That was probably done to minimize the switching transient pop when the mic is keyed and the 4.7 uf cap charges. This cap does not need to be more than twice the value of the first coupling cap in the radio. In most cases all you need here is a 1uf cap unless the radio has extensive audio mods to pass more bass.

    This circuit also takes out some RFI protection found in better versions of the D-104 like the Silver Eagle. It has a choke on the audio output line with a bypass cap. There is also a bypass cap across the input of the stock pre-amp. If you add one to the FET circuit, it must be very small in value or it will kill the treble response. Often all you need is between 100 and 220 pf across the gate to bypass RFI. Using a larger value cap in series with a pot here, will create a treble control. Most of these ideas can be seen in the schematic for the 576-M6B. If you want more bass from that pre-amp just replace the 120K resistor in series with the tone control, with a 1 meg ohm or use a larger value variable pot.

    The trick with melting the wax around the center pin of the D-104 can work when that wax is cracked and is always worth trying before discarding an element. The trouble is that the glue used to hold all the parts together on the element has aged enough to fail unless they were stored under the best conditions. Lots have lost the seal around the diaphragm to case and that can be fixed but the bigger issue is the glue holding the crystal to the case under the foil. Unless the glue holding the corners of that crystal to the case and center pin are solid, the vibrations placed on the crystal suck because both volume and bass are lost. Also, be careful not to put any pressure on the pin when melting the wax.
     
    #13 Shockwave, Jan 13, 2019
    Last edited: Jan 13, 2019
  14. Slowmover

    Slowmover Well-Known Member

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    (Just reading this website is getting expensive. Notch up another “required acquisition”).
     
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