Mood:  a-ok

I got a good deal on a nice-looking D-104 T-UG8 but could NOT get rid of the RF feedback, no matter what I did. I put a FET in front of the existing preamp, replaced the preamp with an entirely different circuit, and hung bypass caps on everything-- nothing helped.

I finally decided the crystal element was the culprit - if for no other reason than it was the only thing left besides the switch!

So I replaced it with one of the small, cheap, easy-to-find electret condenser elements.A I’ve used similar mic elements for years in contact mics for musical instruments in performance settings, and knew that they’re capable of excellent sound and high output. Here's how it went:

Don’t be afraid to take a D-104 apart, the mic element is just a round disk held in place on the round frame by two rubber pieces that wedge in between the element and the frame. It's about 3/8" thick, so a piece of 3/8" plywood does the trick:

About 5 minutes with a sabre saw and a belt sander, and I had a piece that would fit:

The D-104 switching takes a little head-scratching with its break-before-make contacts, but in the TUG-8 at least it's just a DPDT.

The way to wire the switch depends on your radio-- it was more of a pain in the butt for me because my radio required that the mic ground and the PTT ground be kept separate.

One side of the wood was spray-painted flat black (you won't be able to see the back side), and I used the paint-drying time to figure out the switching . Then I hunted up a scrap piece of circuit board and soldered a $2.99 Radio Shack condenser mic element to the board and soldered the wires that had been attached to the crystal D-104 element to the condenser element. I probably should have drilled a hole all the way through the plywood and brought the wires in from the back, but I didn't think about that until I'd already done it this way:

I scooped out a little of the wood behind the circuit board with my Dremel so the board would lay flat against the wood, and then hot-glued the circuit board to the wood-- and then took a foam earpiece off an earbud and hot-glued it around the element to act as a pop filter. The final stepA was to color the circuit board black with one of those big Sharpies so it wouldn't show through the D-104 screen .A These small electret condenser elements are very susceptible to breath pops, and depending on how close you prefer to have the mic to your mouth, a thin earbud foam may not provide enough of a windscreen.A If that’s the case, find a windscreen for a normal PA mic and cut off the front end to fit within the grille of the D-104.A That’s what I eventually did to mine.

So- how does this work? Very well! My radio (an Icom-- no, it's not on 27 MHz) needs a fairly hot mic level so I ended up building a simple preamp for it, but most radios probably will not need it.A The preamp was built on a small piece of circuit board, and mounted on top of the terminal strip in the mic’s base, using the two screws already there.A Try it without the preamp first. The electret elements have a built-in preamp, and are capable of surprisingly hot output levels.A The back of the bubble pack card shows the resistor and capacitor you’ll need to make it work.A In case you need a preamp, here’s what I used:

The low impedance element matches up great, and would to any low impedance radio. It doesn't -sound- exactly like a D-104, but you can change the high/low freq response by changing the value of the capacitor to a lower value-- it will work with just about anything up to 20 uf, but that sounded bassy and mushy on my radio.A I settled on a 0.47 uf, which gave it a lot more "cut" without being too tinny.A You can use that value or experiment with several to get the tone that suits your voice best.

If you want to get fancy you may be able to power it directly from your radio, but I used the 9V battery it had been using anyway-- that allowed me to still use the 4 conductor cable. I'm going to look around for a non-working D-104 I can get cheap and do the same for my Galaxy.A The existing volume control was also used since it’s already there and can be accessed through the bottom cover.A If the output of the mic is too hot, wire the mic’s output to the top terminal, ground to the bottom terminal, and the audio lead of the mic cable to the middle terminal.A You’ll definitely want to use the pot if you use a preamp circuit:

The same thing can be done for just about any mic, such as the Turner +2, Shure 444, and most hand mics.A For these mics a piece of circuit board cut to fit inside the chassis may do the trick without having to use a piece of wood, but it’s not critical-- whatever works, just make sure it doesn’t rattle around the contacts aren’tA able to touch the chassis of the mic.A Switching the battery to the element and the PTT will be slightly different for each mic, but should not be too hard to figure out.

So if you have a vintage mic you’d like to put back into service, or if that Ebay Special doesn’t quitework, give this approach a try.A It’s not expensive, and it’s fun to use a microphone that you rebuilt yourself- and they sound great!

Mood:  a-ok

It's one of the most popular modifications to have done to your CB radio. You'll often hear people say on the radio that their Cobra 29 LTD has had a "swing mod" or "Super mod" done to it. On ebay people often will tell you that the radio they are selling has had a swing modification done to it to make it a "screamer".

So what exactly IS the famous "super modulation" modification?

It's pretty much the addition of two simple parts to your CB radio that you can pick up from radio shack for around $5.

Wow! A modification to my radio that costs $5 and will give my loud modulation? Yep.

Now this modification is not for everyone, and it does require a little soldering, But if you have an old Cobra 29 LTD or Cobra 25 LTD laying around it's a fun modification to learn.

The first thing to know about this modification is that you don't need a special "kit" to do it. Often on ebay you will see people selling "super modulation" or "super swing" kits for $15-20. Although the kits will work, they aren't necessary. You can get all of the parts you need for this mod at Radio shack.

As mentioned there are different variations of this modification. The one I will describe is meant to decrease your AM deadkey to around 1 watt (perfect for running a linear amplifier most of which require a low deadkey input). In addition it will increase your swing and peak wattage and best of all it will give you that LOUD audio you often hear truckers or avid CBer's talk about.

Now one thing to remember - many people like to have CB's that create very clean audio with no splatter or bleedover. Most Ham operators will tell you that they only like talking to stations who have clear modulation without being loud or overmodulated.

Many CB technicians can do this type of modification but can also make the necessary adjustments to give you both a LOUD signal without being overmodulated but this requires specialized equipment that most CBer's don't have available.

Do not do this modification if you are someone who wants clean, clear modulation. Doing this modification to your radio may cause your radio to have bleedover into speakers, neighbors TV's etc.

And now for the warning:

WARNING: Modifying your CB radio is illegal. I don't promote it or condone it. I'm merely providing information. In addition I make no guarantee to the validity of any of this info. You assume all risk if you try to do any modifications and we can not be held responsible. I'm not a CB technician so this information is being provided by an amateur unskilled individual. Proceed at your own risk.

Okay - now that we've explained that let's continue.

What you will need for this modification is two parts from radio shack -

1)A 220ufA (16-25 volt) electrolytic capacitorA

--(If this part is not available I have also used a 470uf 35VDC capacitor with okay results)

2) 100 or 200 ohm (1/4 to 1/2 watt) resistor

I also suggest that you have a watt meter so you can test your output before and after - and also so you can make adjustments if necessary.

Now - different value resistors offer different resistance, so I can't tell you exactly which resistor will be perfect for your installation. Some resistors will give you a 1 watt deadkey, some will give you a 2 watt deadkey. A pack of a couple costs $0.99 so you might as well buy a couple different values and that way you can experiment if you first choice doesn't work out.

Next thing you will need to do is to remove the screws for the top and bottom covers on your radio.

Now we will go step by step

1) Flip your radio upside down so the speaker is facing up.

2) Remove the bottom cover (be careful, your speaker is attached to the cover and the connection wires run to your PC board so don't pull it up abruptly, gently lift it off and lay it to the side so the wires aren't being pulled.)

3) Now you should be looking at the component side of the PC board. You will see that the board has a lot of small labels on it in white lettering. Look toward the rear of the radio and locate JP36.

4) Once you have located JP36 you will need to remove it. To do this you will need to flip the radio over, remove the top cover, and unsolder each end of the jumper on the solder side of the PC board.

To locate the ends of the jumper on the solder side see the picture below.

5) Once the jumper is removed you can fit the legs of your electrolytic capacitor into the empty holes. (VERY IMPORTANT NOTE: The electrolytic capacitor has a NEGATIVE and POSITIVE SIDE to it. When installing make sure the negative side is installed closest to the back of the radio.)

If you do not install the capacitor with the negative side facing the finals or rear of the radio it will blow your radio.

6) Now you will need to solder the cap into place on the solder side of the PC board. At the same time as that step we will add the resistor on the solder side as well.

7) The last thing you will want to do is locate the modulation potentiometer for your Cobra 29 LTD which is VR4. Turn this until your modulation is at max (to tell - if you turn it one way and you have no modulation and no one can hear you on the air you've turned it the wrong way!)

8) Some people recommend adjusting L14 for maximum power, but in most cases after doing the modification your swing should be better than before and your radio much louder so trying to squeeze a couple of extra watts is not my recommendation.

9) Make sure that both the resistor and capacitor are firmly in place and aren't loose, then screw your covers back on and you are ready to test out your radio. (A watt meter is needed to see the results of course.

Many people do this modification because most amplifiers like deadkey input of 1-2 watts and most stock radios have output of 3-4 watts (not a good combo if you want your amp to last a long time).

Some people want to be able to turn the power down for running an amplifier and then turn it back up to run without one. There is a way to do this and add variable power to your Cobra 29.

Basically you would do the modification above - but when you solder in your resistor you would also need to solder a wire to each side that is long enough to reach the front knobs of your radio.

Find the back side of your RF gain knob - it will have two wires coming off of it. Clip those wires and then strip a small section off of each and solder them together.

Now you shouldn't have any wires running to your RF gain knob.

Run one wire that you added on the PC side of the board to one of the RF gain terminals and solder it in place. Then run the other wire to the other terminal and solder it in place. Make sure to use the same terminals that the original RF gain wires used.

Once done your RF gain will now control your variable power. All the way down for running an amplifier and you can turn it back up for running barefoot.

Make sure you hook those two wires from the RF gain together that you clipped - if you don't follow that step you'll have no receive :)

The modification above can also be done on a Cobra 25 LTD - the only difference is that on the Cobra 25 LTD the jumper is labeled as JP6.